i'm gonna be blunt here and say that this does read as a little ignorant. i'm on the much older end of gen z (1999) and i was very much an outdoor kid. it was hard to get me inside, i had a scooter, skates and a bike, i was notorious for climbing trees higher than any other kid dared, i was always on our trampoline.
but then i grew up. i didn't have many friends in school, the few i did have lived too far away or were never over, and the other kids in my street stopped playing. i also got hit badly by depression when i was 12, which has only gotten worse over the years, and have chronic fatigue on top of that which means no energy. i still love warm weather, summer is my favorite season, but i don't have the energy to do the things i did as a kid. i would like to ride a bike, but that's also just not something i can afford now. i can't go for walks because they quickly take a toll on my body, and they also don't stimulate me enough so i just end up bored. and i also just can't find enjoyment in anything i used to like outdoors anymore because mental illness has fried my synapses.
it's not so much "do you like going outdoors" so much as it is "can you go outdoors". the economy is a nightmare these days; people are having to get jobs a lot younger and juggle them with school. rural spaces are fewer and farther between, gas prices are up if you want to travel to forests etc. most sports and clubs require entry fees etc. bikes cost money. and, especially after covid, gen z displays the highest rates of mental illnesses like anxiety and depression than any other generation. and the healthcare system(s) and society refuse to move with those rates. that means less people in our generation have the energy or the motivation to even go outside to begin with. plus, for older people in our generation (and others) there just isn't much of anything aimed at us. playgrounds are always designed for kids and teens.
there is one park near ish my street. it's just been rebuilt. before that, it was vandalized and destroyed twice. the other is a five minute walk away but is just a lot of empty field. the other is much further and also a lot of field save for ramps for teenagers and a children's playground. there's a big forest within driving distance, which i used to love going to, but i can't drive, and i wouldn't feel safe/comfortable walking there alone anyway. same goes for the nature reserve right by my house, which is often littered and, especially in summer, frequented by groups of teens or drunk men. people have died there. i think how safe women in particular feel out alone is also a factor to consider, especially here in the UK after sarah everard.
so yeah, i don't mean this in a rude way, but i think there are a lot of factors you haven't considered, and the "issue" isn't as simple as you think, that's all !!