As pointed out downthread, a lot more people on earth don’t have FB than do.
I’d also wager plenty of people who’ve stopped using it still technically “have” an account but never use it.
So how do you define that “the majority” use Facebook?
First subtract China where it isn't available and you're down to a possible market of 6.35 Billion. But then start subtracting the number of children in the world, the number too poor to spend any money on anything FB would be selling or advertising and random other places where it might be blocked.
That you just ignore the country with the largest population because Facebook doesn’t operate there is a big tell.
Also, why would you assume the kind of products people might sell and thus their pricing? I’ve seen (and bought!) stuff online for ~ 11THB. 35 US cents.
You can say a lot of people use Facebook and that’s fine. But if you’re going to say “the majority of people” you really need to define which people you’re talking about.
But to be even more blunt. FB no more cares about people spending 35 cents online than Apple cares about people who only want to/can buy a phone that cost $100.
For the markets that Facebook is common in, it has enough of a user base that it can be an all-in-one for a small business.