The code is considered IP of the corp and they probably have rules around how or where IP should be shared, access controls etc.
It's a misguided policy that hurts morale and leaves a tremendous amount of productivity and value on the floor. And I suspect that many of the policies are in place simply because a number of the rule makers aren't aware of how easy it to share the code. Look how many in this thread alone weren't aware of inherent distributability of git repositories, and presumably they're developers. You really think some aging career dev ops that worked at Microsoft for 30 years is going to make sensical policies about some software that was shunned and forbidden only a decade ago?