At this point, Bitcoin is fully mainstream and the biggest fools have bought in. People hoped that the Trump election would mean a new giant pot of dumb money (government/tax dollars) would buy bitcoin, but now that they've realized Trump will just issue his own crypto memecoins that bet is unwinding.
I don't see where the buying is going to come from in the future. Every cab driver and retiree and stay-at-home-mom already knows about bitcoin. Maybe Tether prints another imaginary 10 billion dollars to buy bitcoin and prop up the price though, so it could still maintain for a while.
Sure, you can create a new blockchain, but you probably won't overtake the first and most popular, however good your tech is. Also, your comment suggests, as it is often the case, that new blockchains are created not because they are better than all other cryptocurrencies, but rather as a pump-and-dump scheme, and that's the primary reason the whole field has such a terrible reputation.
In any case, first-mover advantage is another reason why it's highly likely Bitcoin will remain the cryptocurrency with the largest market cap.