It's insane that those subscriptions don't remove ads. That's the only thing I would even remotely consider paying for on any meta product.
In the current state those subscriptions will just show your friends that you're a huge loser who's willing to pay for custom backgrounds.
People who pay subscriptions are exactly the sort of people you want to advertise to the most since they've signaled they have money. It's like flashing a big wad of cash in a seedy bar.
Unfortunately, Meta’s ad business is so effective that they would need to charge hundreds of dollars per year for an ad free service just to keep revenue stable. I suspect anything less than $25 per month would be loss making for them.