Consider the opposite direction: what if you want to message someone? What if you haven't messaged them in a while? Imagine you have seven messaging apps installed, some of the names you've forgotten ("Discord", is that obviously a messaging app?). Imagine you know that they're reachable somewhere just not exactly where.

I honestly have never had this issue. It's really about focus and effort. If the person is important enough, I will most likely remember how to contact them. I also mostly use email for all important communications so that remains searchable. The other chat apps are all for casual friends and acquaintances that if lost, well so be it.