I found multiple questions about this within several last year:
How to search only unanswered questions with an open bounty ?
How can I search for bounty questions?
List previously featured questions
Advanced search criteria for bounty questions?
Can we get some better bounty hunting tools?
Most of answers boiled down to two ideas:
- Use hasnotice:1 answers:0 closed:0. It's imperfect, but what can we do...
- Go and browse featured manually or with limited filtering options
Why it was never implemented? It sounds like reasonably straightforward thing (and without any obvious downsides)
Update 1
I was under impression that a lot of feature prioritization is driven by community. It looks like people interested in it. I didn't see anybody opposing it, but it wasn't implemented within last 3 years. That's the main reason for my question.