Just because they're not getting paid in cash, doesn't mean they're not getting paid.
If I go to a fair and buy a bunch of tokens that I then use to play some games, then the people that run the games turn those tokens in for cash - are they token sellers? Of course not! They're game providers and the tokens are just a medium, similar to how I go to Google, to search and pay them with a bit of my screen space to show ads - Google then turns that screen space in for cash with advertisers.
If you're looking at things from a pure "where do the USD come from?" point of view, then sure they're an advertising company - so are TV stations, newspapers, the sides of highways, buses, etc.
Realistically, it's possible to see that a company can have an indirect source of revenue, and not all companies make money from their primary purpose.