Why? The source is open to the public?
It was always meant to be a trademark, even if they ended up losing that particular battle. It was deemed to descriptive and generic to be trademarkable, IIRC. The OSI published their criteria anyway, enforced it as much as they could, and really publicized the term over the years. Of course they get to define it.
there's nothing wrong with source-available, but source-available and open-source are not equivalent.
It's not open for them to use.
To argue otherwise is to confuse a window with a door.