Lots of endowments come with strings attached. We made a charitable donation to a local university for them to buy some specific science outreach equipment, they bought it.

This all seems reasonable to me. If you want my money or things, you’ll have to use them like I suggest.

If you don't want to abide by the conditions of a gift - don't accept it.

That's an ignorant simplification of how property ownership works. For example, defeasible estates are not a new or rare thing:

https://en.wikipedia.org/wiki/Defeasible_estate

Granting land conditionally such that the ownership reverts once the condition stops being met is very much a thing. I can't find the full details of this particular case, but it sounds like the property went through a long sequences of transfers that probably make the legal situation tricky.

The intent was to gift a park.

Why can’t gifts have contracts?