While I agree with the sentiment, keep in mind that circumstances change over the years. What made sense (and what you've believed in) a few years ago may be different now. This is especially true when it comes to business models.
When backed by a company there is an ethical obligation to keep, at least maintenance. Of course legally they can do what they wish. It isn't unfair to call it bad practice.
Ethics are not obligations, they are moral principles. Not having principles doesn't send you to prison that is why it isn't law. It makes you lose moral credit though.
Claiming that you’re entitled to free R&D forever because someone once gave you something of value seems like a great way to ensure that nobody does that again. You got over a decade of development by a skilled team, it’s not exactly beyond the pale that the business climate has changed since then.
However, almost every open source license actually DOES warn that support may end. See the warranty clause.
With open source it does. If an indie open sources and get a baby or lose interest, it is understood as fair to suddenly stop maintenance.
When a company surfs on the open source wave to get contributions, grow penetration, then smoothly slows maintenance and announces to get a license, that's gaming the open source community.
See the numerous cases of popular open source repo where the parent or new parent company took over to gain the user base without any respect for the maintenance if not development aspect: community fork and take over the community.
Mariadb, a more recent illustrative example of that is the hashicorp drama that occured when investors decided it was time to gear towards profit at the detriment of the community that largely contributed to the tools.
You're saying that a commercial company has an ethical obligation to do work for you in future, for free? That doesn't follow from any workable ethical system.