Tl;Dr is that matt mullenweg saw that other people were making money from free open source software, and his capitalism boner is trying to fuck everyone over.
He has control over both WPEngines competition and the non-profit Foundation, and is using his Foundation position to try extort his for-profit company's competition. Typical CEO behaviour.
Basically, he's a CEO and therefore thinks every dollar on earth is his by right. I think the best summary is that he's using his competing positions at the non-profit foundation to benefit his for-profit company.