Life happens.
I have created one bounty in my entire time at SF ... and ended up not "paying" it. I hit the site several times a day during the first 3-4 days of the bounty, and no workable answer was given. Then, something came up, and I ended up travelling for a couple of weeks. During that time a great answer was given, but I was otherwise busy and was not checking in at SF.
When I returned to the site and found the great answer, the bounty had expired. I had to apologize to the guy!