There were and are good reasons not to use Erlang. It's much (like an order of magnitude) harder to find developers who know it and almost impossible to find developers who can use it well (e.g know what a gen_server is). Much Erlang code I saw at Ericsson were technically written in Erlang but very much resembled imperative style code you'd find in a Java project. Erlang is also not very good at interacting with the surrounding system which is pretty important for a SoC.

I left Ericsson many years ago, but I bet that they are still using ClearCase for version control, FrameMaker for documentation, and that there are still five managers for every developer. Pretty sure they are still drinking the kool-aid, trying to put AI in their exchanges glued together with TypeScript.