Someone keeps deleting "classic-animation" keyword from certain titles

Someone keeps deleting the keyword "classic-animation" from several animated TV shows of the 1990s. I don't know why this is happening, but I know for a fact that I have submitted it as a keyword for many of these titles and it was previously approved, only to disappear later.

On the official help page for subgenre keywords, the definition of "classic-animation" is this:

Animation produced during the 20th century.

That's it. No more specific constraints or limitations are provided. Nothing vague or subject to personal opinion, either. A very simple and objective standard.

The keyword exists under both the movies and series sections. There is no reason given in that definition why 1990s cartoons shouldn't qualify. Even two out of the three examples from that very same help page are 1990s cartoons (specifically, X-Men (1992-1997) & Spider-Man (1994-1998)).

Most recently, I have noticed the keyword deleted from The Ren & Stimpy Show (1991-1996), The Little Mermaid (1992-1994), Street Sharks (1994-1997), Aladdin (1994-1995) and Animaniacs (1993-1998). Obviously, these were all animated and produced entirely within the 20th century. The keyword applies according to IMDb's own very simple definition. I of course went ahead and submitted the keyword again for all these titles. We'll see if it sticks this time.

If there is a legitimate reason why these titles shouldn't have the keyword "classic-animation", then the definition on the help page should be changed in order to adequately explain how it can apply to only some of the animation produced in the 20th century. Otherwise, the editors should stop allowing people to delete keywords that are demonstrably valid according to the definition provided.