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

I grew up on a farm so every cat that I knew was an outside, nearly wild cat. I noticed people having inside cats as I grew up and I notice that the nature of the inside cats are not much different from outside cats because they bothe share the curiosity to explore. I notice indoor cats often looking out the doors and windows with such curiosity I want to open the window and door and let them go, but it isn't certain that they will return, be able to protect themselves, or keep from threatening others because I do remember the fights between cats that would arise betwen the male farm cats.