If the Altcoin market follows BTC price rally then the bullish market is confirmed due to new FIAT entering on crypto market. If not then the BTC rally today is just the result of altcoin holders that shift to BTC which might result to price pull back in few days. Well, let's see. Grab your popcorn and watch here:
https://cryptowat.ch/markets/coinbase-pro/btc/usd/15m many altcoins are shitcoins, have no use in the real world, are meaningless projects and every day shitcoin more appear than to become great competitors of shitcoins that already exist and many investors already realize this. That's why people sell their altcoins to buy bitcoin. Look at what these altcoins promise, you get scared. People will not sell their bitcoins to buy shitcoins again
I'm a "serious" holder of a couple or so altcoins, and then give a handful more for casual fun, and I still have to agree with you. Even if I wanted to, I couldn't use the majority of the coins I use. Monero, maybe, okay, if I really needed to keep things super private, but then I'd have to convince people to accept it (and I have a hard time doing that for Bitcoin already!). Litecoin, I like it and I could use it, but Bitcoin's still a first option. There's no place I shop or pay at that accepts LTC and not BTC.
Save those few, sure I got coins with interesting ideas but at the end of the day, nothing close to the practical use I have for Bitcoin. And that's proven by my own personal spending history which is 100% in BTC.
So, OP, duh altcoin money eventually flows back to BTC!