Well, the only things I can think of are:
 - people are tired of the current system and wants something better.
 - people wants to have anonymity even if it is just a bit better than fiat.
 - people want an easier way of gaining profits fast.
 - people got curious about the new trend and wanted to get a piece of the future.
 - people convincing other people with broad explanations about the crypto world.
 - and of course, the never ending forks that gives free money.

That's pretty much everything i can think of really.

Number of reasons are there which are causing bitcoin price to increase. i am sure that bitcoin price will continue increasing for along time, because still bitcoin has too much potential and people are still accepting bitcoin and are also investing money in bitcoin. i am sure that very soon will  see the price of bitcoin trading above 8000$ in next few months.

the else thing that is contributed to the price is bitcoin is a new technology for some people which is know bitcoin at the early time and now with the increasing of the price, i am sure that many people will come to the bitcoin and they want to join in bitcoin. the boom in bitcoin is because the price is increase significant in this year and makes many people become curious and they asked what is going on with the crypto currency now and why bitcoin price is rising to fast.

There were a multitude of factors:

price increase caused more people to buy, which causes more price increase

fast price increase caused media to cover it more, which caused more people to buy it, which caused price to continue to increase.

I guess that first and most important thing would be earning easy money from fluctuation of its price. Most of people deal with Bitcoin only because it is easy to earn extra money with it. Second thing would be that people understood posibility of Bitcoin and start supporting it. Bitcoin have a bright future and people see it. Hope it will continue to be like this.

Of course that this year has been the most incredible for bitcoin, and not only for this coin, a lot of altcoins increased a lot during this year, probably this has been the year of the "crypto boom" because a lot of people discovered bitcoin and most of them started using cryptocurrencies.
I hope that next year is going to be a good year for cryptos too, maybe we are going to see bitcoin over 15 thousand dollars, omg, just think about it, that is insane.

In addition to what you said ( demand and supply) there is also another factor that influences​ BTC price which is ACCEPTANCE ; I mean when bitcoin is accepted to be a payment method by big shops and online stores , then its price will surely increase

I think that's part of it: the speculative frenzy. CNBC is pumping it. Everyone is talking about it. Prominent people are saying it will be worth 6 figures a piece someday. And then you add in the altcoin effect. Newbies (and even old timers who aren't maximalists) pour money into altcoins and ICOs, and this further dries up BTC supply, as these markets mainly trade against BTC. The altcoin markets take so much liquidity away from the BTC/fiat markets, helping supply on the exchanges to stay low, making the price go up even easier.

It's a big feedback loop. Some might call it a "pyramid" or "Ponzi" scheme, but they'd be wrong. Having said that, a lot of cryptocurrencies are highly risky to hold. Even BTC's price could drop by 50% in a day and old timers wouldn't even blink an eye. The volatility now is nothing new for those of us who were here in 2013.

I think another main reasons is that people are feeling that the fiat system is failing, in my country the inflation is supposed to be at 3% per year but I buy my own stuff and I have realized that in just the last 5 years the price of almost everything went up 50% or more.