As the question Am I allowed to ask for a rep boost indicates, offering a bounty without realizing that you will no longer be able to comment or vote seems to not be atypical. This is exactly what happened to me as well. It would be great if points given away in bounties did not count against using basic functions of the site.
By offering a bounty, you're giving something up in exchange for... well, advertising.
What exactly you give up depends on what you have, but at very least you're giving up some amount of status and potentially privileges on the site as well.
Why should someone who has earned reputation elsewhere be immune to this when someone else who has worked hard to earn the same privileges here must give them up in exchange for the bounty?
If the trade-off isn't acceptable to you, then... Don't offer the bounty.
You already get a free 100 reputation when you join from another site in the network and you have sufficient rep.
There is one practical reason why your proposal would not really work out: It would generate confusion. Some users with 13 rep can comment/vote, others can't.
There is also a strategic reason: reputation is 'expensive', it takes time to construct and if you want to have privileges you need it. If you discouple privileges and reputation, the latter will lose its worth. Someone's reputation is indicative of that person's experience.
If you want a question so badly answered that you are willing to look like a noob to the site, feel free to spend your reputation on bounties.
If you want the priviliges, do the work. Answer questions. It is give and take.
If you want keep the possibility to vote and still get your question some attention, you will have to find other ways to get your answer more attention and get it answered:
- posting it in chat,
- asking in meta how to make the question better,
- providing more info,
- doing more research,
- rephrasing the question