I am now trying to give a serious answer.

Today's kids are a product of the society and their parents. This mean that kids are not at fault, and that kids lack of activity is complicated.

In all western countries activity level goes down. The USA is sadly at the bottom.
One structural problem here in the USA is liability.
If you go to playgrounds, trails, etc around the world you will see fewer signs about how dangerous everything is, but more important.
Schools, local government, gyms, organizations do not need to be afraid of getting dragged to court due to liability.

I took my son to my old school yard, it has trampolines and slack lines, but no sign. My son's school yard has signs and is safe.

Liability is part of the structure in the USA and will not change. So I do not see kids getting more active.

I agree. I lived in Europe for 3 years, 3 different countries, and liability issues really struck me as different between here and there. Much more personal responsibility was expected. I'd routinely see something and think, you'd never see that in the states as the lawyers would be all over it. Children were also WAY more independent.