The pricing of a billboard is based on projected impressions but is decoupled from the billboard’s actual impressions. You pay the flat rate based on projected impressions. It doesn’t subsequently matter if an army of robots passes through and views the billboard 10,000 times, because the original projected audience should still see the billboard. You’re getting what you paid for. It’s also possible the projections are erroneous, fraudulent, or that the actual impressions just don’t follow the projected impressions for some other reason. This is the advantage of advertising online—if you pay for 10,000 views, the ad runs until you get them.

Contrast the billboard with an online ad: If you pay for 10,000 impressions, and 9,000 of those impressions end up being automated traffic, then you’ve effectively lost 90% of your advertising budget. Like you mentioned, ad buyers can and do account for this, so it’s not clear that it’s as big of a problem as this thread is making it out to be. The theory I see thrown around is that Meta and Alphabet are tacitly allowing this bot traffic to continue (or even that they are responsible for it themselves) because it allows them to sell another round of ads, but if this is what is going on it isn’t clear why firms would keep buying ads that aren’t converting.