I've seen plenty of places with this mindset.

Instead of risking their data in the motherlode of hacks occurring against Github they setup on-premise Github/Gitlab/Bitbucket/etc. then let the servers go unpatched, stay several versions behind, don't bother setting up authentication roles properly and give people more access than intended.

There are plenty of places doing on-premise right, but I definitely trust Github over the average undermaintained on-premise installation.