Well, it's just the free speech issue all over. Either you censor speech or you risk people saying things that you really don't like. This is exactly the same situation: Either you go FOSS, with all the benefits it entails, and risk getting forked by a major player or you go proprietary and risk not getting adopted at all by major players and open source enthusiasts.

Don't get me wrong, I feel with the Elastic team and I can understand why they're unhappy (even if I don't agree with their pettiness). I also don't particularly like the move Amazon did here. But that's why we want free software: If the current owner of the software does something you don't like, you can still use the software. That's the whole point.

And you're still free to pay Elastic to manage a cluster on AWS for you; Amazon might have forked the project, but it's still the customer that needs to switch to OpenSearch.