People rotate out of Bitcoin into Altcoins when they think Bitcoin is heating up & close to a top. It’s almost like you get the best of both worlds. Ride the Bitcoin wave of fomo & rotate into Altcoins to catch Altseason, take profits there, before the whole cycle comes to an end. We are not in Altseason yet, it will be later this year.
That's how it works usually when bitcoin dominance is reducing.
However we also need to remember that there are some institutional investors that aren't rotating to altcoin and the fact that altcoin is already too diluted doesn't help either.
So expect there to be some of altcoins that doesn't pump. Mainly the ones with low trading volume because the market just don't care.