Say you don't understand opportunity cost in software development without saying it.
I won't delve too deeply on the obvious: most "competent Linux sysadmins" have a very over-inflated sense of their own skill set, and tend make for toxic team members.
Most software development shops are in the business of developing their particular software, not deploying and self-managing DVCS, much less hosting, monitoring etc...
Sure, could one person set up a Git/GitLab system? Absolutely. Can they operationalize it effectively? Not really... the bus problem is a thing and anyone that thinks tying the entirety of a system's uptime to one individual is an operational improvement over GitHub's outage SLA is deluding themselves.