They do some of this. For example, the silver Necromancer badge is awarded when you "Answered a question more than 60 days later with score of 5 or more"

http://stackoverflow.com/badges

You can put a bounty on your hard question if nobody answers it.

You can, but you are penalised for doing so.

Penalised? You spend some imaginary points and in return you get more chances for a good answer to your question... That's a fair tradeoff, if you ask me...