Their trips were paid for by people who expected discoveries of various kinds to yield a net win (land, minerals, food, whatever).

The explorers' dreams are of less importance than their benefactors' expectations.

Good point. But the same applies today--the benefactors like Musk, Isaacman, and Bezos all expect to gain from the exploration, maybe not in terms of money, but at least in fame, or as they put it, "advancing human achievement."

Right. But 60 years ago, putting a human on the moon was universally seen as "advancing human achievement". I would argue that right now, where we are not actually about to build a moon or Mars base, putting people out there is not widely seen as "advancing human achievement".

Sending someone to Mars without them dying (and maybe bringing them back) will be a huge step. There's so much we can do on and around Mars, however, without anyone being out there, and some of them are also likely to be huge advancements.

Similarly for the asteroid belt. Yes, it will probably need humans out there eventually, but there's a massive, massive task of mapping and exploring it that can and almost certainly will be done without launching humans into space.

You're not entirely wrong when extrapolating from historic trends up to-say- 1999. But the price of launching humans into space has gone down dramatically as is this century (to the point where privately funded LEO missions have become viable), and looks to be going down rapidly in the near future. Space flight looks like it might be entering a period akin to Moore's law in IT.