Having two accounts are allowed and apply to the bounty campaign but today they are now restricting to avoid joining alt accounts to give chance to the other users who would like to join. Abusing this kind of opportunity is prohibited by the forum and also have a penalty and give you a negative trust.
Thank you for pointing this out. This is exactly what i thought about; You mentioned rules from different bounty campaigns which restrict participants from using alts, but if we take the example of someone using alts in a campaign where manager didn't set that rule. Note that there is no mention in forum official/unofficial rules about alts joining campaigns but almost all tagged alts were breaking campaign rules at first place. Here am not encouraging anybody to use alts joining the same campaign as it's somehow a kind of sheatting , but just trying to explain my thoughts for better understanding how things work here.
. It will create fatigue which lead to lack of ideas and might result to spamming later on. 
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