But you don't have to develop anything. There are plenty of ready-made excellent tools you can just drop-in. The main fallacy is that what Github does is actually useful, or that the pieces it integrates are useful. 90% of Github is subpar for any given purpose. Consider all the possible types of software being developed and all the different release flows and support/issue flows, how could they possibly be shoehorned into a one-size-fits-all? Yet people try their damnest to do exactly that.

To do software development you need (A) issue tracking, (B) a clear release flow, and (C) a deploy mechanism that's easy to use. A is a drop-in tool with lots of alternatives, B is unrestricted since Git is very flexible in this regard, and C is typically included with any cloud infrastructure, unless you're doing on premise in which case there are also drop-in tools.

A, B, C are three distinct, orthogonal topics that can and should be handled separately. There's no logical reason to shape any of them after the other. They have to work together, sure, but the design considerations of one must not affect the others.