All the stuff using Android intents, out-proc COM extensions in Windows, XPS in macOS, are other relevant set of examples.

I assume you are kind of new to the computing world, OS IPC is how we extended applications almost 40 years before shared libraries became common feature across all major operating systems.

Naturally with them being around, shared memory in-process was much easier, and less resource intensive. IPC calls require processes, which take more kernel resources, and context switch.

Microservices isn't a new concept, rather re-branding.

Sun had as marketing quote, "The network is the computer", exactly because of how it used to be.