I pay for Spotify and Google Play. If either one of them starts showing me ads, they're gone. It's not me I'm worried about at this point. It's my kids.

Some are likely far over that threshold. However, I doubt everyone willing to pay 10$/month is worth more on average.

Facebook makes $7 per month per user in the US and Canada. So, it's likely fairly close though.

But it doesn't matter if you lose money on those people. The $10/month easily carries all costs even if 0.1% of users pay and the rest gains them zero. (At least, back when I did the math in ~2015, when they were probably a bit smaller than they are now.)