I agree. I grew up in a tiny town where basically all parents had to work so we (the kids) had more or less no adult supervision of any kind. There were no mobile phones, no internet, no consoles (that any of us could afford anyway), sometimes not even a football, so most of the kids spent all day out inventing games and fun activities with a key around our necks. Everything could be a toy, everywhere could be a playground.

As a kid I never even considered an adult could contribute in any way to my free time and to the degree to which I will enjoy it. Of course they had a contribution but it was more akin to teaching an autonomous car to drive rather than you driving the car yourself. The end result is still a functioning car, but the implications of each case are vastly different.

Maybe the particulars of the situation made it possible. Small, safe town with friendlier people, fewer distractions available, more relaxed legal framework, fewer dangers out there, etc. But the implication that you need adults to build and maintain an environment in which kids can play is only valid if that's the way you lived it so it's the only way you can imagine it. It is sufficient but not necessary. There are plenty of other ways that don't involve parents to build their kids' playing universe. And having just one more possibility invalidates the premise of the original comment.