The advertisers are bluffing when they threaten these boycotts. They're not going to stop advertising on google, facebook, twitter, etc., which these days probably represents a majority of their advertising budget and even more of their ROI. They'll make threats because it costs them nothing, but all the platforms need to do is say "no" and that would be the end of it. Even better: immediately ban the accounts of companies that make these threats. They won't receive any more of them.