Partly because there are no decentralized PoS coins that are alive.

The developers of PoS coins either sign blocks as valid (e.g., Peercoin) or create new "updates" with checkpoints (e.g., Nxt).  In other words, they solve the history-rewrite problem by acting as a central authority.  


https://yourlogicalfallacyis.com/burden-of-proof

I said that no one had proved that the "nothing-at-stake" problem can be solved--I never said that it was unsolvable (although this is my opinion).  Until it can be proved to be impossible, I must accept that it may be possible (and I do).


Considering that you wrote "if you know how to kill it," when I never made that claim, and then employed a logical fallacy "why don't you do so?" (burden of proof), I disagree: they weren't really honest questions.