That doesn’t match my experience if your bar is really as low as “won’t throw you out for not buying anything”.

Obvious anecdata, but within an easy walk or bike radius of me (a couple miles) there are 3 public libraries, something like half a square mile of parks, a few public basketball courts, a few public tennis courts, a public baseball field, a bar over the baseball field that welcomes children (it’s one of the veterans things and has board games and what not), at least a dozen other businesses that don’t care if you buy anything, and your usual litany of Walmart kind of places that can’t be bothered to track who is buying and who isn’t.

I don’t have any issues finding places to hang out for free, and I use them, but they’re pretty sparsely used so it’s not as 3rd space as it used to be.

Eg I walk my dogs most mornings, and I rarely see more than 1 other person at the park or dog park at 7 or 8am.

It feels to me like 3rd spaces are disappearing because people don’t use them, rather than people don’t use them because they don’t exist.

Consider yourself very lucky if your public libraries are not daycare for the homeless.