Bonds bought between '10 and '22 are heavily under water at the moment. It doesn't make sense to sell them now at a massive loss. 

Maybe this chart is just reflecting the fact that many of the purchased bonds lost up to 60% of their $ value. 

 I've heard that is indeed largely the case.

But, whether it makes sense to sell the underwater bonds right now? - hell yea. They are nowhere near the bottom in BTC terms. There is no bottom.