A combination of (0) having disposable income, as you said, but also (1) lots of free time to browse social media, which in combination with making money might

A combination of (0) having disposable income, as you said, but also (1) lots of free time to browse social media, which in combination with making money might mean maybe not working so hard; (2) low enough standards to spend a lot of free time on social media, and in case of twitter probably not "connecting with family back home"; (3) suggestible/gullible enough to click on ads instead of doing product research; (4) not technically competent enough to just block ads; (5) maybe, conspicuous-consumption/status/consumerism focused enough to buy the kind of high-margin products that justify ads. How these are weighted I dunno. But yeah, sounds pretty much like chattering class ;)