I think it's that we just have more things to do and people aren't going out and being as social these days. Even just a couple decades ago there wasn't much to do if you wanted to stay home but now there are tons of entertainment options if you choose to not go out. This is especially true if you are someone who has confidence issues and can't get laid that easily, why go out and risk likely rejection when you can just stay home and jerk off to porn?