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

It depends on the place you live and the type of cats. If you live in the suburbs or rural areas, and the cats are run-of-the-mill breeds, then it's very common to see the cats living outside more than inside. Unless the weather is inclement.

However, if you are talking about Persians where a kitten can cost as much as 300usd, for starters, you do not expect to see those Persians walking along the roads or crossing the fields any time soon. On top of that, if it's a question of keeping Persians in a city environment, other factors like safety from car accidents would keep all the cats indoors. Probably on a leash, too.