Personally, I have two semi-open species, which granted aren't the same as closed species but they're similar. I run them as "you can basically do whatever you want with them, here's a good starting point if you can't think of any, now go off and do great things." My only major rule is that I want something out of getting more than one and I want to be notified when you create any of them so I can keep track.
Personally I would be more invested in closed species if any of them ran like that.
But they don't.
Most of them have a discord/da thing (which I cannot or will not use), and they have literal pages of lore you must read before even creating one, such that if you want a closed species, you have to ONLY use them in the provided world. Personally, I find that utter BS, if I want to use my Forget-Me-Not angel in the same universe as my own angel and demon characters then freaking let me. (Not sure if FMNs have that sort of rules but assume they do for that moment.)
But this isn't my CS, it's yours. If you feel like you want to create all that lore, go right ahead. It is how CSes tend to work, after all. I just feel like it's far too much effort on my part and extremely limiting on the receiver's part, which is why my species are Semi-Open instead of Closed.