You seem to be speaking about Big Tech as though they were the ones who are buying physical advertisements, rather than selling them. I think Google, Facebook, Twitter, etc. mostly place digital ads for businesses, which would not be affected by a ban on physical ads in cities. The parties affected by a ban on physical ads like billboards in large cities would mostly be the large companies who buy them. Small businesses (a bakery, a bookstore, a barbershop) aren't buying outdoor advertising at the rate that large companies are, and so if anything they'd be on a more level playing field.
You picked small business that wouldn't buy billboard ads. I see local restaurants and hotels on billboards all the time: they are targeting non-locals who might use that business if they only new how close it was.
I don't remember seeing too many of those billboards, but I'll take your word that they're out there. Most of the billboards I recall seeing are telling me all my dreams will come true if I go to a tribal casino. I still think most people just look up local restaurants on their phones. I can't imagine the lack of billboards would hurt too many small, local restaurants.
