A significant portion of larger sizes is likely due to how Google handles shared code across its iOS suite. They rely heavily on a shared C++ backend (using tools like J2ObjC or similar internal transpilers) to keep logic consistent between Android, iOS and of course the web. When you pull in the gmail dependency from the internal monorepo, you are most likely pulling in the entire visual stack for Google meet, chat…
This is more like the what causes these apps to be so large, but when you ask why then you see that they simply do not care about the amount of space they take on users’ devices. There’s no obvious effort to reduce app size with modular design, it simply feels like they don’t care.