> I only encounter this in Rust when doing anything web-related.

It's probably because anything web-related requires so many things no readily available in the language or in the standard library: anything from databases (sometimes different breeds of databases) to templating to serialisation (possibly multiple types of serialisation) to rest or graphql to...

Just serialisation (which is almost invariable Serde) will pull in at least 54 dependencies (if you only use serde and serde_json). A framework such as rocket which provides all that, and more, will pull in ... 332 dependencies :)

Edit: Calculation is invalid, see https://news.ycombinator.com/item?id=24024671