Summary: it's cultural. Rust likely inherited the practice from Nodejs, who inherited it from Ruby. I think in Rust online spaces in particular there is also this undercurrent of "you're not smart enough to use certain parts of the language, so download libraries that handle that stuff for you."
https://www.youtube.com/watch?v=E82ly38YEEQ
Summary: it's cultural. Rust likely inherited the practice from Nodejs, who inherited it from Ruby. I think in Rust online spaces in particular there is also this undercurrent of "you're not smart enough to use certain parts of the language, so download libraries that handle that stuff for you."