Why is web code so dependency heavy?

The bevy game engine is roughly 400 dependencies. Leptos, a Rust full-stack framework, is over 700 by itself. This seems to be the case for most web applications, not just in rust.

What causes the dependency count to inflate like this? Is it just a natural consequence of some attribute of web code, or were there mistakes made in the fundamental design of the web that need to be resolved?

I have a few theories:

1. Boilerplate for resolving platform differences
2. Codegen and parsers
3. Error handling, logging, and monitoring