99.9% of small businesses do little to no advertising. I can’t recall seeing an ad for a single one of the small businesses I am a customer of. 99.9% of ads I get are for megacorporations and national brands.
I know people who do moderation for the advertising side of social platforms and they say that more than half of the advertising submissions are done by small businesses. They said that the estimate is around 90% of small businesses use internet advertising in some capacity. There's a bidding mechanism, though, so more big business ads may be shown; especially if you live in a populated region. But that's just a numbers game.