Besides is illegal for an individual to enter a bounty with multiple account if caught would be penalized so that case is solved.
In theory, yes, but we all know full well that most altcoin bounty campaigns will accept anyone - shit posters, plagiarizers, alt accounts, etc. The bounty managers do not care enough to check. Just like the bounty participants, they only care about being paid, and not at all about whether or not they make half the forum unusable in the process. Hell, some of the bounty managers enroll their own alts in their own bounty.
And if you check it the real bounties that pays in bitcoin accepts only high ranking members so there is a benefit to rise in your rank
Again yes, but these bounties aren't usually the ones responsible for the majority of shitposting and spam.