Why should they do that? Could be a form of spam which can be filtered by clients imo. 

 For example Redbull could use part of it's advertising budget to push own notes up on nostr by zapping from different lightning wallets. Maybe it is similar as  promoted content on Google or favebook. 

 Yeah, this is a real way to game the system. Zaps have to be interpreted with web of trust of some kind in mind, or just with some healthy skepticism. It's one thing to show fake zaps on a post you're already looking at, another entirely to promote posts based on zap numbers.