The problem with a homegrown system is that every developer working within it will see it as a barrier rather than a cost saving. Whenever they can't do something that's trivial on Github/Gitlab it'll be a reminder that the company would rather save $xxx/year than make their job easier.

Ultimately, having a simple, well-integrated, industry standard stack that includes the same tooling every other company uses is a perk of working at a well-funded or profitable company. People leave for less.