I think you nailed it in the last sentence. AWS will one day be able to extract near monopoly profits due to costs of migration. I expect the ES didn't realise

I think you nailed it in the last sentence. AWS will one day be able to extract near monopoly profits due to costs of migration. I expect the ES didn't realise how popular it'd end up being so went open source, and later realised they'd shot themselves in the foot but knew they'd rub people up the wrong way if they went closed source so they kicked the can down the road... And here we are