Why don't kids play outside anymore?

As a kid, I was always playing outside. I lived to be outside and be climbing a tree or playing a game of football or wiffleball. It wasn't just me though. The entire neighborhood of kids would be together in a vacant lot or field and be playing pickup games or tag. Nowadays, I don't see any kids outside. I'll be going on my evening run and see an old vacant field that my friends and I used to play in and I wonder why a new generation of kids aren't out in it playing like we were. My guess would be that they're stuck inside playing their video games and on the computer. I'm surprised that more parents don't make their kids play outside and it saddens me to think that kids today are missing out on the joy of playing outside.