+1 (as a millenial) ... especially given that setting up a git server for non-OSS company code isn't too much of a challenge really. also, no need to self-denigrate this reasonable opinion in preemptive obedience.

GitHub is way more than just a git repo host. It manages code reviews, merge (pull) requests, and has an entire CI/CD workflow engine in it. Replicating all that is a challenge that most orgs are not up to.