The self-entitlement in open-source has to stop. This is only one example of a maintainer quitting. There are many more.
And the shaming of projects who want to make money to sustain their projects also has to stop. Nothing is free. Somebody is paying for it in time, resources or money.
If you don't like what a project is doing, or how they're monetizing, don't use it. Move on.
I agree.
Playing Devils Advocate it sounds like the options, for them, would be to stop providing a non-paying version entirely.
I understand where they are coming from but providing an open source version that won't get timely security updates feels like it would be more trouble than it's worth to use.
If they only want to work on a version that pays for their time I'd suggest they make the whole thing closed source.