Many altcoins are down in value as holders of these altcoins sell them and buy BTC instead - it sounds so promising, BTC is the future, the rest is not.
you say that as if you don't believe it!
the thing is, majority of the altcoins specifically the top ones that everyone hypes these days, are worse than bitcoin. you just don't see the issues in them because they are not used. they just hype it and pretend they are better, more promising, better scaling, etc. but when it comes to reality they all fail, harder than bitcoin. google crypto kitties and see how it crippled ethereum for 3 days now.
and yeah, bitcoin will crash like it always does after a big rise. but in the end it will pick up again and continues rising because it has that "real adoption as a currency" not just speculators who are in it for short term.