I think you have to ask why Spain went with a small, relatively unheard-of Ukrainian Yak operator in the first place.
It wasn't for the prestige, I'll bet.
Maybe the Spanish did a thorough assessment and thought that hauling its troops to and from Kabul this way was the safest and most efficient.
Then again, they might have just gone for the cheap option. And maybe they're now learning the hard way that safety is never as expensive as an accident.
Given that the Ukrainian investigation has already highlighted queries about potential breaches of operating regulations by the carriers, I suspect that there's not going to be any shortage of blame on both sides.
In the meantime it will be the genuinely safe and respectable outfits from Ukraine which lose out.