TL;DR: Cofounder of open source project says super popular platform using their project needs to pay up for inane reasons. Chaos ensues.
In summary:
WP Engine is one of the most popular third party platforms built on top of WordPress.
They have a link and images on their webpage referencing that they are built on top of Wordpress (this is legal).
The former cofounder of Wordpress said that they are illegally using the Wordpress trademark.
WP Engine sends Cease and Desist.
WordPress Cofounder doubles down, blocks WP Engine and demanded WP Engine pay licensing fees for using their branding.
This pissed off a lot of people.
WP Engine sues. For a lot, including extortion, abuse of power, and asserts the cofounder of WordPress has criminally made false statements to the IRS.
The Executive Director for Wordpress resigns, presumably in solidarity with WP Engine and the community.
Company runs a hosted Wordpress service that competes with wordpress.com. Wordpress (i.e. CEO Matt Mullenweg) wants a cut and is trying to strong-arm them. People are upset with this.