Elasticsearch got popular, and now Elastic wants to reap all the rewards and make money off the product. They're free to do that, and create restricted-license or closed-source versions for future enhancements. But the community doesn't have to buy into that and continue to contribute to what is no longer truly an open source product. AWS is forking it and continuing with the original, truly open source license.
This is pretty much exactly what happened to MySQL, and now we have MariaDB, which is a better and truly open source product.
AWS does plenty of things worth criticizing, and one can even criticize them in this particular instance for not working with Elastic to provide more support to whatever it was they were asking for. And Elastic may very well have a legitimate gripe about trademarks. But yanking the Apache license out and moving to a more-restrictive license is not the right solution, and is not what everyone who contributed to building the product signed up for.
You can't create an open source project, wait for it to gain market dominance, decide to be less open source, and expect the community to continue contributing.
Elastic shot themselves in the foot and now they can either revert their decision or get left behind as the community moves on to what will ultimately end up being the better product.