Compilers and test suits do scale (at least for C/C++ and Rust, which is what I work with). But I think the parent comment referred to consumer applications: games, word processing, light browsing, ...

(Though games these days scale better than they used to, but only up to a to a point.)

I find that most tools I write for my own use can be made to scale with cores, or run so fast that the overhead of starting threads is longer than the program runtime. But I write that in Rust which makes parallelism easy. If I wrote that code in C++ I would probably not bother with trying to parallelize.

Test suites often don't scale, actually. Unit tests usually run single-threaded by default, and also relatively often have side effects on the system that mean they're unsafe to run in parallel. (Sure, sure, you could definitely argue the latter thing is a skill issue.)

In theory, do you need a single machine for any of that, or would it be cheaper to use a low-availability cloud cluster? Tests are totally independent, and builds probably parallel enough.

Only a small percentage of computer users are programmers.