Because running a parallel process is often difficult. In most cases, the question becomes:
So, how exactly is my app/whatever supposed to spin up a parallel process in the OS and then talk to it over IPC? How do you shut it down when the 'host' process dies?
Not vaguely. Not hand wave "just launch it". How exactly do you do it?
How do you do it in environments where that capability (spawning arbitrary processes) is limited? eg. mobile.
How do you package it so that you distribute it in parallel? Will it conflict with other applications that do the same thing?
When you look at, for example, a jupyter kernel, it is already a host process launched and managed by jupyter-lab or whatever, which talks via network chatter.
So now each kernel process has to manage another process, which it talks to via IPC?
...
Certainly, there are no obvious performance reasons to avoid IPC, but I think there are use cases where having the compiler embedded makes more sense.
So, how exactly is my app/whatever supposed to spin up a parallel process in the OS and then talk to it over IPC? How do you shut it down when the 'host' process dies?
Not vaguely. Not hand wave "just launch it". How exactly do you do it?
How do you do it in environments where that capability (spawning arbitrary processes) is limited? eg. mobile.
How do you package it so that you distribute it in parallel? Will it conflict with other applications that do the same thing?
When you look at, for example, a jupyter kernel, it is already a host process launched and managed by jupyter-lab or whatever, which talks via network chatter.
So now each kernel process has to manage another process, which it talks to via IPC?
...
Certainly, there are no obvious performance reasons to avoid IPC, but I think there are use cases where having the compiler embedded makes more sense.