My expectations was far less on "bitcoin-only", but people here are usually new to crypto and don't know much about altcoins yet.
It doesn't matter what you belive will happen on BTC vs altcoin in the long run, we live now. Current returns on altcoins vs BTC are insane and there is no other way that can double one bitcoin faster. (regardless of BTC/USD) The (unlikely) risk of a bitcoin-killer is here and the bitcoin protocoll would never able to adapt fast enough. It's 100% impossible that f.e we will ever see PoS in bitcoin since there are far to many people (miners) interrested in keeping it the way it is.
Ignoring altcoins is like igoring the most innovative part of crypto. People were able to see the potential of bitcoin, but now some of those are so in love with bitcoin that they can't see the potential in altcoins. Altcoins don't need bitcoiners to buy them, there are sill enough people left that haven't heard of crypto yet.