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

I grew up having many outside cats on the farm. There were enough cats to the point where it was practically necessary to keep the cats outside. We had people dropping off boxes of kittens at the end of our driveway because they couldn't care for them, yet it was easy to keep a great number of outside cats at the farm. We would feed the cats the old milk that couldn't be sold to the dairy company and the cats were free to hunt the mice and shrews in the hay lofts so the cats lived a pretty happy life being outdoor cats. However, with outdoor cats it is inevitable that there will be fights over mates, territories, and food. So the solution to that is to keep cats in their own agreeable territories, which is inside, to prevent them from competing for necessities. I think that cats have started to be brought inside to prevent the dangers of conflict between other cats as well as mating with another and making their owner drop off a box of kittens at a farm a couple months later.