Services allow you to interop with all languages, they let you avoid worrying about threading models of the program your operating within, and they don't have access to all of they sandbox the code being run allowing you to avoid worrying about the code doing something nefarious with access it gets from running inside your process. On top of this, people just seem to be fat more okay with not having source access to a service than they do using proprietary libraries (which from a security perspective makes sense to me).

If there was a standard threading model, language agnostic interop with clear evolutionary properties (perhaps a channel based one), and a generic mechanism for sandboxing libraries folks could use then maybe they would consider providing libraries more. Some sort of hybrid between COM, wasm, and optimized in process grpc is more or less what I'm trying to describe. This doesn't exist, however, and moving your library out of process solves this issue neatly so it's not a surprise that's what's happening.