Indoor vs Outdoor cat - Why are there more "house" cats now?

Probably for the same reason we don't see children running all over the neighborhood without adult supervision. We worry that something will happen to them and we want to keep them safe. It's never been an issue with my cat. She was feral (though use to being around people) and followed me home several times. I finally gave in and allowed her to stay. She's never made an attempt to go back outside.