Re: Can't or wont?
Even if the full details are classified, surely they should be able to provide something in an unclassified setting. I think the reason is because they can't point to anything useful these programs have done, but don't want to admit it publicly. In a closed session they can admit that but claim "we're working diligently to address the shortcomings but need more time" and it would provide the senators cover to vote for it, claiming "we heard enough in the closed session to believe it is useful" without anyone being able to question them.
I think Feinstein doesn't want the closed session because she knows it will be too easy for senators to vote yes on this given that cover. Historically she has supported every spying program, but at some points even enablers of the surveillance state have to reach their limit.