You only see the market moved that way but you haven't see that sometimes it is going oppositely. The time you see the scene of bitcoin pumps > alt dumps usually what happens.
But there are times that you can see it like this way.
Bitcoin pumps > alt pumps, vice versa and so on while it is randomly changing without any reason on why it happens. Probably affected by news depending on the coin that has good and bad news.
Not the Crypto or ALT coins control the market, it is the growing investors globally, not to mention the volume of investment put in into the Crypto Market. one should note that, Market is Volatile, anything can happen at the trading market, price value may goes up and goes down, it is unpredictable.