I think Paramount made a wise choice, back in the day, to say that only the STAR TREK TV shows and movies counted. There were a ton of novels and comics, some good and some bad, but to try and juggle all of that and make it fit would have been a nightmare.
STAR WARS is a bit of a different story, with its different levels of canon. The EU was generally accepted as canon, but the movies always were the top dog (and even occasionally referenced elements from the books and comics). It was sort of a “you can generally accept the spin-off materials as canon, or choose to take them or leave them).
Nowadays, of course, canon has been smashed with a hammer, and the people producing the live-action material have exceeded the worst of the worst novel/comic writers, because they can’t even get the most basic elements of the universe and the characters right.
Imagine a “canon” line, if you will. Writers lined up for jobs, in the hopes that their stories will be deemed canonical. The lucky ones are at the front of the line to write TV and movies. The next group gets to write spin-off novels and comics. At the back of the line are the fanfiction writers, followed by shippers and slash-fiction writers…and worse.
Somehow, people from the very back of the line—or who were just driving past the line—saw all the hubbub, wanted a piece of the action for themselves, and were able to skip right to the front of the line, with no problems or dissent. And everyone else was told to go home.