Isn't the reason that you are asking this question the very cause of all problems related to Bounty Campaigns?
Bounty Campaigns are not designed for people to earn money for minimal work, the idea is to empower and reward people who are interested in their project to help advertise it to the world. But, where there is money, there is greed. Now we have 'people' (I'm sure that a large portion of these 'people' are just 1 person handling multiple accounts) joining campaigns without caring for what they join or the ideals of the project (that's how scam projects get their coverage) and are in it just for the money.
I don't think Bounty Campaigns are a waste of time, I think that in principle they are awesome. However if you're looking at it from a financial gain perspective then you're part of the problem that is damaging crypto in general. Better to get involved with fewer projects that you really can believe in and support them honestly and properly.
Yes, that is a big problem, there are tons of these farm accounts controlled by a few people joining any campaign which as you said gives them coverage. If only real people was joining then most of the shitty campaigns would not have many participants. Also the bounty campaigns don't care too much, or not at all about the quality of the posts.