Yes, let's blame the person that structurally has less power in the dynamic for having that power imbalance used against them.

Of course you can try to negotiate for more. Enough people want to work at a startup however that if you ask too much, you'll get passed on, and they'll just hire the next candidate who doesn't act so entitled to a meaningful piece of the founders' pie. It's exactly the same phenomenon that lets the big game studios chew up and spit out engineers: there's always someone else willing to take the job for less, or even just put up with the status quo.

That's a massive part of the problem, and telling people to negotiate better doesn't address it — or even acknowledge it.