What does Gmail actually loads when it's "loading Gmail"

Question

And why does it load every time? (Why) Can't it be cached on my browser?

Answer 1

Almost all websites cache of data on your local device. With Gmail they are updating all the changes since the last update. Email could have been sent and received. Messages could have been labeled or archived. Some of these changes take place behind the scenes.

Remember many people use Gmail on multiple platforms. It is not unusual to have people logged into the service on the work computer, home computer, and phone at the same time.

All this is made even more complicated if the user has decided to use the offline option, where a copy of the data is on the machine, so that the user can read and manage email when they don't have internet access.

Answer 2

It loads all functions in background—code, styles, queries, and lot of others.