JavaScript isn't a generic term. There aren't lots of JavaScripts. Just the one.

If Oracle is going to lose the trademark, which it probably should, the reasoning could be better. How about the fact that Oracle doesn't really offer a service called JavaScript. Isn't abandonment a reason to lose trademark?

"Google" has become a generic term for search engine, like "Jello", "Kleenex", "Kool-Aid," etc. "JavaScript" isn't like that.

Maybe I'm misunderstanding. Can someone clear this for me?

The grounds for cancellation in the USPTO letter are from both abandonment and genericism (and “fraud on the USPTO”), and Deno’s open letter to Oracle mostly touches on the abandonment issue.