I'm really trying to remember a national park that was "free". There are various small parks/historic sites which are free largely because its a statue/gravesite/etc but I can't remember one of the actual parks having free entrance in quite a white. There are a number which don't have gated entrances, but they still have honor system signs to the effect that you need to put money in the drop box.
The national forests OTOH, yes they are largely still free, but they are also heavily managed, frequently with commercial interests (ex, ski resorts at the top of the mountain, logging rights, etc). Which has resulted in the push to reclassify a number of them as wilderness, which has its own issues if you happen to be anyone but a birdwatcher (ex hunter, fisher, mountain biker, trail maintainer).
I think I had this conversation not long ago too. I used to frequent smokey mountains a lot in the 1990's. Even then there were fee lots but plenty of ways to bypass them, which I as a starving college student was pretty good at. OTOH, they don't really have a fee because a couple of major roads that are hard to avoid run right through the middle of the park.
So, to me the recent moves sound more like they are closing all the loopholes around avoiding the parking fees (ex parking on the road rather than in the lot) which were there to replace the entrance fees.
The national forests OTOH, yes they are largely still free, but they are also heavily managed, frequently with commercial interests (ex, ski resorts at the top of the mountain, logging rights, etc). Which has resulted in the push to reclassify a number of them as wilderness, which has its own issues if you happen to be anyone but a birdwatcher (ex hunter, fisher, mountain biker, trail maintainer).