How do you think people write and compile software for any embedded or other low-powered architecture out there? The vast majority of hardware in use around the world today isn't desktop class, and emulation works just fine for building on those.

Cross compilers are nowhere near the same as Docker on ARM Mac building x86 Linux containers. The biggest difference: no one expects you to be able to run your MIPS binary on the machine you built it on.

Edit: although sometimes you can through qemu.