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.
The business people may be happy enough, but the Global Moderators, Administrators, and Eldest members of this forum probably would not be. Most of them have more than two accounts. Hilarious here has an account for his/her Global Moderator role on this forum, and then a second account for personal stuff (like the conversation here). It's likely he/she has even more accounts that aren't used very often
Nearly all of the most senior leaders on this forum have many alternate accounts.