Now that’s a big assumption.

Yep, that's why I said TEND to be shut-ins, not ARE.

And if you have kids, it’s not about not being single, it’s about having kids.

Well single people TEND to not have kids.

Single people go out with their friends, go on trips, movies, restaurants, all that. Those who don’t just aren’t outgoing.

Yes, the ones that aren't shut-ins do all of that. I agree. But when you are single, you arguably have more opportunities to save money than people with a SO do. For example, a single person can choose to live with more roommates to save money. People who are not single TEND to want more intimate privacy and just live together without other roommates. This is me btw. I used to live in a house with 4 other roommates. My rent was $300 per month divided out between my roommates. I got a GF. After a couple years, the GF and I wanted to move in together. My rent is now $700 per month after splitting it with my GF. I now have $400 more dollars per month in expenses than I did when I lived in a house with my friends.