it is the bubbles bursting once again. you seem to have forgotten how all this was started. let me remind you.
when bitcoin had issues about its scaling and the war was at its worst in the early 2017, the altcoins used this to start pumping. you can still find the topics saying "blank is going to replace bitcoin because bitcoin can not do blah blah and it is dropping down to $10".
so idiots who read these topics rushed to invest and dumped their bitcoin and bitcoin price went down while whales were accumulating bitcoin.
now that idiots know what they have read was big lie, and as they got dumped on and lose money in altcoins and also lost the chance to buy bitcoin, they are now dumping their altcoins to go back to bitcoin. that causes bitcoin price to go higher and alts get dumped hard.