The FAQ on bounties:
1. The bounty period lasts 7 days. Bounties must have a minimum
duration of at least 1 day. After the bounty ends, there is a grace
period of 24 hours to manually award the bounty.
2. If you do not award your bounty within 7 days (plus the grace
period), the highest voted answer created after the bounty started
with at least 2 upvotes will be awarded half the bounty amount. If
there's no answer meeting that criteria, the bounty is not awarded
to anyone.
Taken together just want to ask simple question why the bounty are not awarded automatically is not clear some times.
Eg. web kit scrollbar not chaging until i hover over it when changing themes