Well there are numerous reasons. Maybe you want one business and one personal account and not to mix the two. Maybe you might want to sell or talk/promote something that is considered controversial by some or maybe you want to discuss politics etc without it effecting the way people perceive or do business with you here.
Hm, sounds like a quite good reason. Good point.
But you agree that there is no need to have more than 5 accounts for sure? The persons who participate in the bounty campaign with multi accounts, they most likely have more than 5 accounts, and they are posting from all 5 thus increasing the spam level on the whole forum. I would say that technically possible to create limitations based on MAC/Hardware address, for instance, there are 2 accounts allowed per one device. The business people will be happy enough and bounty-cheaters will be down.
Well sure there's probably not many good reasons to have more than a handful of accounts but the exact number is of course subjective, but yeah, the people with dozens - and in some cases hundreds of accounts - create them just to milk bounties and campaigns for all they're worth and when this happens the quality of their posts are usually severely diminished. Check this guy with his 200 accounts all making shitposts for example:
https://bitcointalk.org/index.php?topic=1912475.msg18975980#msg18975980That's what happens when you get greedy. Maybe he should have stuck to a handful of accounts and it might not have been so blatantly obvious what he was doing. Now he lost all those accounts. Was it worth it? Probably not. As I and others have said the merit system severely restricts how many accounts people can likely have but as we've already seen multiple times people are still trying to farm and trade merit between themselves and their alts.