Its odd at first, but springs from economic principles, mainly sunk cost fallacy.

If you invest 2 days of work and did not find the root cause of a bug, then you have the human desire to keep investing more work, because you already invested so much work. At that point however its best to re-evaluate and do something different instead, because it might have a bigger impact.

Likelihood that after 2 days of not finding the problem, you wont find it after another 2 days is higher than starting over with another bug that on average you find the problem earlier.

This sounds incorrect. You didn't find it but you're gaining domain knowledge and excluding options, hopefully narrowing down the cause. It's not like you're just chucking random garbage at Jenkins.

Of course, if it's a difficult bug and you can just say 'fuck it' and bury it in the backlog forever that's fine, but in my experience the very complex ones don't get discovered or worked on at all unless it's absolutely critical or a customer complains.