Maintainers are certainly free to adopt a "take it or leave it" attitude if they want.
But most maintainers (including Elastic) don't want that. They proudly declare that their developers and users are a community, and they're steering the community to produce a great and open project on an ongoing basis. The maintainers certainly have a responsibility to follow through on such promises - or at least, if Amazon is correct and they aren't following through, they have no right to complain about a hostile fork.
Promises without consideration (e.g. unpaid) aren't enforceable.
I help out by sweeping Amazon's yard everyday, for free. "Thanks!" they say, "Any time!" I reply. But years later, I decide to stop. Amazon cries out in anguish "But you have a Responsibility!", and threatens me that if I don't clean their yard... well, they'll do it themselves.
Free maintained software suits Amazon, and some organizations / foundations provide it. Seems to work as consulting services advertising (BTW which incentivizes hard-to-use software, lots of complicated features, jumbled together... ever seen a large foundation's open source project like that?)
Some businesses fund these foundations directly, but minimally, and there's a certain... reluctance. Perhaps an unmet need there...?
Amazon is welcome to fork and welcome to point out that they might be better for users than Elastic. But the issue here is that Amazon--like many others before them--are asserting a 'right' that simply does not exist.
I don't think Amazon's trying to claim that Elastic has done something legally or morally wrong. They just don't feel Elastic has lived up to their standards for community management, so they're going to take their ball and go start a new community with higher standards.
But most maintainers (including Elastic) don't want that. They proudly declare that their developers and users are a community, and they're steering the community to produce a great and open project on an ongoing basis. The maintainers certainly have a responsibility to follow through on such promises - or at least, if Amazon is correct and they aren't following through, they have no right to complain about a hostile fork.