People need to reread this classic piece from 2001 every so often: https://www.joelonsoftware.com/2001/03/23/strategy-letter-iv...
As a regular user, you are probably using 10% of all features available.
Gmail barely has any features, which haven't changed since it's inception. Most of the code is in the cloud.
This might be true but most of time its just bloat no one uses.
[dead]
Don't blame the users. Unless Google have hidden a copy of Crysis inside the Gmail app there's no hidden functionality which should come even close to requiring hundreds of megabytes.