I suspect you’ve nailed the answer: it’s probably not easy, although it’s also possible that it just hasn’t ever had a lot of attention paid to it because it’s been generally fast enough for their user base?
But in commercial production environments, CI pipelines tend to want to build everything from scratch every time, and that slows everything down. Rust has the same issue. Both languages, by default, compile all their dependencies from source, rather than obtaining precompiled artifacts from a repo the way some languages (like Java) do. And their compilers are slower than e.g. Go's. As the article mentions, various kinds of caching can help with that, but that's extra stuff you have to manage and deal with.
I'm not sure this is a bad thing, though. Haskell co-creator Simon Peyton-Jones coined the unofficial Haskell motto, "avoid success at all costs". I tend to agree with that. It would be difficult for Haskell to maintain its conceptual edge if it were a mainstream commercial language.
You can also limit it with an env var. I have capped mine at 10GB.
You can put the `cargo clean gc` command on a daily/weekly schedule then, or configure the `gc` option in your Cargo config. Or set `CARGO_UNSTABLE_GC=true` in your shell init. Or all of the above.