Of course, only because Apple and Google did everything in their power to prevent people sending files directly between devices. When you have a duopoly that splits the population in two parts and they can't send files between them, of course users will rely on messaging apps to share stuff.

Short story: I did a long trip across two continent with my wife. Me with an Android devices, her on iOS. We did backup our photos in our own private cloud but guess how we had to quick exchange photos while in the wild (no wifi and sometimes no network)? We couldn't. Because Google and Apple did everything so we couldn't.

Google wants to your data and fought for the cloud. Apple don't want Android users to easily partake in some data exchange with iOS users (you gotta buy your ticket to their jail). So sad you don't realize how backward that is.

I don't think that is the reason. I think people tend to choose by default the same app they are communicating on. It just feels more natural and straightforward.

The same thing used to happen (and still continues) with emails. Even with shared cloud drives synchronized to their computers an awful lot of people are still sending files by email/teams/ticketing systems.