It never was about trademarks ....
But that's just not something you get to control when you license your software as GPLv2. Some people are gonna use it in ways you don't like.
He should have just done an marketing campaign about why you should host with Wordpress.com instead of WP Engine. Instead he's torched an insane amount of goodwill for seemingly no return.
It's like the difference between getting an account on a Mastodon instance versus a specialized Mastodon instance hoster.
WP Engine is a pure commercial WordPress hosting service, while WordPress.com also has a personal blogging service stapled on.