I'm a bit disappointed by all the good guy/bad guy judgement going on here on HN, when both players are working with the market forces to get the best result.
From AWS' perspective, taking an OSS Project and offering it as a hosted solution is legally fine.
Elastic isn't happy about the fact that AWS make more profit from their OSS product than themselves, so they recognize that OSS isn't their best approach anymore, and do it differently.
AWS decides that forking and maintaining the their own OSS version is more profitable in the long run than paying license fees.
What changed since Elastic's original license choice? Hosting an SaaS version was possible back then, but it didn't happen at the scale that it is, so it was more of a theoretical problem. Now it's a very practical problem.
This is a bit of a simplistic take, and there seem to be a lot of side shows (like trademarks), so more details lurk in the shadows.
If I were to try to make a value judgement, my premise would be the flourishing OSS is a good thing. AWS's actions have have driven Elastic to make their product no longer OSS, which is not good. OTOH they maintain an OSS fork, which is good.
But the interesting broader question is: would it have been beneficial for OSS if Amazon were paying some license fees to Elastic, for an OSS product? I think we need to find some model whereby OSS shops are not forced to rely on the whim of a giant to make their money. Whether this can be done sustainably without restricting usage rights remains to be seen, IMHO.