Distributions generally package the versions of compilers that are needed to build the programs in their package manager. However, many developers want more control than that. They may want to use different versions of the compiler on different projects, or a different version than what’s packaged.

Basically, people use it because they prefer it.

different goals

the rust version packaged in distros is for compiling rust code shipped as part of the distro. This means it

- is normally not the newest version (which , to be clear, is not bad per see, but not necessary what you need)

- might not have all optional components (e.g. no clippy)

but if you idk. write a server deployed by you company

- you likely want all components

- you don't need to care what version the distro pinned

- you have little reason not to use the latest rust compiler

for other use cases you have other reasons, some need nightly rust, some want to test against beta releases, some want to be able to test against different rust versions etc. etc.

rustup exist (today) for the same reason why a lot of dev projects use project specific copies of all kinds of tooling and libraries which do not match whatever their distro ships: The distro use-case and generic dev-use case have diverging requirements! (Other examples nvm(node), flutter, java etc.).

Also some distros are notorious for shipping outdated software (debian "stable").

And not everything is Linux, rustup works on OSX.

I'm a Debian Developer, and do some Rust both professionally and for fun. I restrict myself to using only libraries and tooling from Debian. The experience is quite OK. And I find the Rust language team to be quite friendly and sympathetic to our needs.

Rather, what makes it hard is the culture and surrounding ecosystem of pinned versions or the latest of everything. That's probably in part the fault of Rustup being recommended, I agree. But it's not nefarious.