Earlier quoted context omitted.
It is not OSS if it does that, because you limit what the software can be used for. It becomes just source-available software. Being open-source to get a user base and then change the license isn't that great, they should have started as proprietary and that'd have been fine.
I don't think they were disingenuous here: I think they probably chose a license somewhat randomly (acknowledging it wasn't copy left probably?), then got developing. Down the road, they saw someone using the software in a way they didn't like and decided that as they were now bigger, they could afford to get a license drawn up with their values in mind. I doubt there was a nefarious plan to use a licence for it's re…
You use Apache 2.0 when you explicitly don't want copyleft. But here's what's great: copyleft wouldn't even stop Amazon, so they have to use SSPL which is a proprietary license masquerading as copyleft.
Also, one way they were clearly outright reneging on their promise was that Elastic explicitly promised the community that the parts of the codebase that were Apache 2.0 licensed (the 'open core') would never be made proprietary. They broke that promise for this move.
And what's doubly hilarious is from a business perspective it's an awful move. It won't stop Amazon from making money - they'll just fork 7.1.0 and develop under Apache 2.0 like they just did, and keep operating their service just the same. And by the way, it's Amazon's right, legally AND ethically, to be able to operate AWS Elasticsearch for profit - just as Elastic is right both legally and ethically to use Lucene as a necessary part of Elasticsearch.