It's not about losing your trademark but about someone you don't know and can't yet trust, potentially using your trademark for their own goals. It'd be like letting someone use your name and social security number to identify themselves. You wouldn't want that even if it's a friend, let alone a stranger you never met in person.

Let's say the IRGC, Mossad or NSA is behind that developer of the Notepad++ on Mac clone and would love to piggyback on your trademark name in order to push a spyware infected app on to some targets. You don't know them and can't trust them so you don't want them using your name because that would backfire on you.

There's plenty of precedent with this in browser extensions, where once they become super popular they end up being sold and bought by some shady Israeli PE or ad-tech company with ties to Mossad. You don't want your name or trademark anywhere near this, if you value it, so you'll have to call out and ban everyone who tries to use it without your explicit permission.

This isn't the developer trying to be a dick to other developers, this is the developer exercising common sense and self preservation.