it's not a webpage. It's an application that happens to run on browser platform.
If you downloaded a regular software and the exe file was 5MB that would be considered small nowadays, yet if a web application fetches that in JS it's considered large.
(sidenote: not defending the gifs they're just idiotic)
It depends what you can do with it. Downloading a full 5MB app just to be able to scroll down and show text and a few images can be seen at big. Why not use a webpage ?
If you downloaded a regular software and the exe file was 5MB that would be considered small nowadays, yet if a web application fetches that in JS it's considered large.
(sidenote: not defending the gifs they're just idiotic)