I didn't see a case made for self-hosting as the better option, instead I see that proposition being assumed true. Why would it be better for my company to roll its own CI/CD?

I worked at a bank that self-hosted GitLab/runners.

As the AI bubble goes sideways, you don't know how your company data is being held, CoPilot uses GitHub to train its AI for instance. Yes, the big company I work for had a clause to forbids GitHub from using the company's repo from AI training.

How many companies can afford having a dedicated GitHub team to speak to?? How many companies read the contracts or have any saying??

Not many really.

Yeah sure, cloud is easier, you just pay the bills, but at what cost??