Rust does allow for safe signal handling, but it's sort of the same way that it allows for safe and correct interrupt handlers for people writing os kernels (signals are basically interrupts, just from kernel->user instead of hardware->kernel). You're basically constrained to no_std and have to be very careful about communications with the rest of the system using lock free mechanisms.

It wouldn’t be as bad if it was that simple :)

If handling a signal was equivalent to handling concurrency then it wouldn’t be as much of a problem.

IIRC a signal can take over execution of a running thread, so it will completely invalidate any critical sections etc. You cannot access any shared resource easily, cannot allocate memory and a lot more restrictions of this form.