Who even uses external CIs anymore? GitHub and gitlab ones are great otherwise you have plenty you can deploy yourself.
But for some companies paying extra to be able to blame someone is crucial.
Also it was to show that some ppl dont understand the offering of products they use.
Bespoke CI/CD solutions are great, especially if you're the author and tailor it to the business, for a certain size and class of use case.
As a business though, it's hardly ever worth the investment/maintenance and ongoing operational cost vs. just externalizing it and dealing with the consequences unless it is your business or a fundamental part of how your business is delivered. Thus, generic (but extensible) solutions are the happy medium.