People will spend Bitcoin if some products are designed that can be bought and sold through Bitcoin. Or Bitcoin will be accepted as a payment system. Banks will accept Bitcoin as a means of transaction. Currently, some banks in the world are not accepting Bitcoin for transactions but as collateral for loans. However, the day when banks accept Bitcoin as collateral for loans as well as for transactions, Bitcoin will be used as a currency for people to spend in the world. That is, people are now only saving Bitcoin as a store of value but not spending it. This only increases the popularity of Bitcoin but the value does not increase in that way. If Bitcoin is used as a means of spending and transaction of goods, then of course its popularity will also increase greatly in value.

No one would be willing to make such a foolish decision right now. Because every investor and every person knows what the price of Bitcoin can be in the future and how much Bitcoin can make us in the future if we hold Bitcoin now. Despite this advantage, no one would ever be willing to trade with Bitcoin, especially not me.

Another thing is the volatility of Bitcoin. Due to the volatility of Bitcoin, it seems impossible to trade with Bitcoin. Suppose you buy a product right now and the price of your product is 40$ equivalent in Bitcoin and after some time if the price of Bitcoin decreases a lot, then you will have to pay much more Bitcoin at that time. So for this reason, it seems impossible to trade with Bitcoin right now.

Trading with your bitcoin is different than spending your bitcoin.

Trading your bitcoin can cause profit or loss but basically it's not spending and you won't likely lose all your bitcoin with one trading position. With spending, at the time you broadcast your Bitcoin transaction, your bitcoin gone (of course it needs to get a first confirmation from Bitcoin miners).

You misunderstood between trading and spending.

You can't force anything on anyone, Bitcoin is free, so people can use it as they see fit. Some people hold Bitcoin to protect themselves from fiat inflation, and many people use Bitcoin to save money, that is, to save time and money. And many people use Bitcoin for their daily purchases,
so they will use Bitcoin according to their price plan and keep it for the future. But this is the only way that I think is the most important thing, people can benefit from it in many ways.

Take note that tax laws are peculiar to the jurisdiction in question. However, if you spend BTC in a region where BTC is taxed, that action would be treated as you sold the coins, so you'd still be subjected to Capital gains tax.
I am not sure why you think spending BTC offers you better privacy, it really depends on if you know what you are doing. It could even put a trail on your back if you spend BTC from your cold wallet, with a large balance. As far as laws in other countries go, as long as BTC isn't banned, then you can spend it through merchants that accept the coin.

I can think of nothing else here except to buy and sell Bitcoin.  Meaning trade Bitcoin and do buy low and sell high. 

It would be hard if we are talking about earning more Bitcoin while we are spending Bitcoin, except we put it in a business where we buy raw materials in Bitcoin, and sell the finish products in Bitcoin.

Spending it for necessities won't earn us more Bitcoin even if there is a percentage commission in our expenses.  The outgoing Bitcoin will always outweigh the incoming Bitcoin in this trade design so there is no profit to be seen here.

Trading is easier said on paper "buy low sell high" but when put to practice they end up understanding it's a more riskier way of earning more money with Bitcoin, volatility is their biggest threat it makes them panic and end up in lose, the wise ones later understand that buying and holding longer to sell off some in future is than hoping on buying low to sell high within short period.

Truth, you earn more by holding (best chance) or trading (lucky chance) spending it means selling off some portions either at lose or when it's overaccumulated, except the person is selling for a more profitable option with potential.

There is actually a difference in buying something with your bitcoins after holding them for a good amount of time and when they have already reached a good value, and buying something with your bitcoins right after you buy it, because most people don't do that and that's the reality. We have to accept it that nowadays, most people buy or invest in Bitcoin for holding since they know they are going to make money by doing this, and making money is everyone's target because it's a necessity for all.

If I buy 1 Bitcoin today for $80k, and keep holding it for 4 years or more and price per Bitcoin reaches $160k and then I decide to use my bitcoins to buy something, then that doesn't mean I bought my bitcoins for spending but I had bought them for holding and now that I have achieved my goal, now I'm spending them. This is mostly what people are doing these days, you will barely find anyone who will use their fiat to first buy bitcoin and then spend those bitcoins to buy something.

To make this possible you will need a Bitcoin based business,
But If you buying of items in Bitcoin is dependent on your ability to sell items in Bitcoin then you may never get to buy items with Bitcoin. where I'm from it may get difficult sometimes to see someone who buys items with bitcoin, outside this forum there are just little individuals willing to do transactions with Bitcoin, if you support the usage of Bitcoin for buying and selling then it should start with you, you don't have to make it dependant on who Is willing to buy from you with Bitcoin first

Meanwhile it's all personal to whom want their Bitcoin as store of value or medium of exchange, I know majority go for store of value and it's basically because majority are after profits and still inflation than other benefits.

Convenience is all that matters to spenders and when they don't find that convenience on platforms offering Bitcoin payments then you won't see them come back. We shouldn't be begging people to spend in Bitcoin but make it so easier that it looks easier, less costly and more convenient spending on Bitcoin marketplace platforms then fiats because right now fiats are winning. if everything was smoother over here then we'll get more people spending their crypto not just Bitcoin alone. To buy anything right now with Bitcoin looks stressful but if we have platforms that can allow you to buy things automatically like you deposit Bitcoin on their platforms then use their wallets for shopping, things might get somewhere. The marketplace wallets will just be used for holding the Bitcoin or other crypto that you want to spend shopping and it might just make things much more easier for people.