Many projects this year are unsuccessful, so it is normal for delays or failures of the bounty, and many bounty won't tell you when it ends. So the longer the time, the tokens in each share. The less you have.
Main issues is Participants who join the campaign. Many of Bounties apply Stake Systems. So, i dont think Long Bounty will decrease your earn.
But, i can conclude that project isn't attract Investors too much. Developer want reach their cap and sometimes extends end time can solve it