I get that Matt based WordPress on open source software initially, but 99% of the work that became what WordPress (and by extension, WP Engine) is today was done by him and his company.

WP Engine contributes nothing back. They're just leaches on an open source license.

They're doing what AWS and the other hyperscalers have done. Making bank on other people's hard work because "pure" open source allows for third party commercialization without compensation. (Or even giving back, as is with WP Engine's case. IIRC, they're not a top contributor to the open source code.)

Shouldn't we be angry at the appropriators that take everything and give nothing back?

AWS is 99.999% closed source. They're taxing the industry and contributing to increased centralization. Much of what made the early web so exciting has been hoovered up by these open source thieves.

Google for taking WebKit, snatching the web, and then removing Manifest v2 amongst other crimes.

Again - I think the community is attacking the wrong person here. Matt acted immaturely, but he's the one that put in the work. Not WP Engine.

Only the extortion (1030(a)(7)) CFAA claim was dismissed, and it was dismissed with leave to amend.

That's actually very cool. In most runtimes the "core" built-ins and standard libraries are immutable. You'd have to recompile them with your changes to get the same effect. Not so with PHP. A footgun, but in this case a useful one.