Celery is genuinely one of my favorite parts of soups that use them. I LOVE the flavor or celery, and it is even better when it picks up the rest of the flavors of the dish.
To answer yours and the other questions about “why this ingredient”, the answer is very simple. Some people like it.
If you don’t, then don’t use it, problem solved.
I mean, the reason is that it’s one of the main ingredients of mirepoix, and most people don’t find it offensive. It’s one of those background flavors that you don’t pick out, but is part of the typical base.
What I’m getting at is that if you don’t like it, just don’t use it. It’s there because whoever made it, decided to put it in.
Now, I’m sure there are all kinds of explanations about the enzymes, and the fiber and so on, but it’s soup, doesn’t have to be complicated. Just delicious :)