Hi,

Bitcoin is the original alt coin, so it is quite logical that its trend tend to drive others'.

But you are right, if we follow the logic of offer and demand, actually when btc goes down, eth should rise. This would be true if cryptos were the man trading factor. But it is not. When the price of bitcoin falls, it is because (amongst other reasons) people are selling their bitcoin. But they do not sell to buy other cryptos, they sell to get back their initial currency (generally speaking, fiat money, such as dollars, euros, etc).

So yes, this will be true when bitcoin are traded for other alt coins. But I hope this won't happen, because, please, remember that bitcoin is NOT a trading tool. 

Recently, the rate of bitcoin and other crypto currency shows a decline because of the decisions of China and South Korea about the limitations of the work of crypto-exchange exchanges. In addition, the price of bitcoin may have been affected by the stoppage of trading on the Japanese exchange Coincheck, which was forced to take such a step because of the hacker attack - as a result of it, NEM was stolen by 400 million dollars.
The bitcoin rate may also be decreasing due to the statements of some large investors. So, George Soros - an American billionaire, speaking at a forum in Davos, called the crypto currency a typical "financial bubble". At the same time, he stressed that the same bitcoin is not a stable means of accumulation, like another currency, and therefore crypto-currencies are just speculation.

it may be because people are cashing out from all those altcoins to come back to bitcoin market.

but the important thing to remember is that IT HAPPENS!
knowing that you can simply prepare accordingly and by acting faster because of anticipation you can become a lot more successful in this market and make more profit.

If you mean driving, that would mean the urge to use or gain financial help from bitcoin. It could also be the urge to learn about Cryptocurrency and not just Bitcoin because bitcoin is based on Blockchain Technology which is currently helping a lot of platforms to revolutionized their programs and become more advance than any technology. Learning about Bitcoin would take interest on how much knowledge you want to learn.

Most of the cryptos are tied with bitcoin's price directly because all of them are traded mainly against bitcoin rather than fiat so when bitcoin will get dumped people will start to sell their other alts for bitcoin to sell bitcoin in panic. And vice versa when bitcoin start to surge, they will start investing their bitcoin back to alts so that they can increase their total bitcoin.

all altcoin is highly dependent on bitcoin
try to you see, when the red bitcoin graphics automatically all altcoin will follow the volume of bitcoin, and it is true that bitcoin is called king, crypto currency in the world. Because everything will follow bitcoin,When bitcoin up or down. it all depends on bitcoin

Bitcoin is actually the progenitor of all of the existing cryptocurrencies.  The progenitor bears most of the damage but some of the damage shall be handled by the progenies.

if the investors in altcoins are panic selling and are in fact exiting to USD through bitcoin, then what you are saying is that the altcoin dumps caused bitcoin price to drop not the other way around! is that what you are trying to say?

because it makes sense that altcoin dumps cause a drop in bitcoin but i don't think it was the case here.

Nearly all other crypto coins are bound to BTC to switch to USD. That is why bitcoin price movement affects the altcoins prices.

Bitcoin is not driving any other crypto currency and that there is no direct relation in between any of the crypto currency with that of bitcoin. However, this is just a general observation that at time when the market value of the bitcoin falls down, the market value of the rest of the crypto coins also falls down and that is because of the reason that bitcoin is like the most popular coin having a huge market.