I think it's mainly software folks who feel mathematical learning it. Mathematicians primarily use it as a linkage and general tool in some context. I feel category theory needs something to latch it on to. Most software based applications seem a little too contrived, unless I have missed something interesting.

Because many people (myself included) find it A) interesting, and/or; B) useful.

Odd take on a post called "applications of category theory"

I mean topology didn't have so many applications 100 years ago, but now that shits everywhere. Math is the ultimate r&d. It's literally the language of causality. Imho it can't not be useful.