We had Jenkins, but it required so much engineering time to manage, secure, upgrade, etc. Then when we hit scaling limits as our team grew, scaling it out to multiple machines took more time and cost a significant amount as we had to have capacity for peak time, which when all engineers are in one timezone is a significant peak compared to, say, the weekend.

We moved to CircleCI and while I have many frustrations with it, parallelism and ability to speed up the pipeline with minimal development overhead are not really frustrations I have. The cost is also minimal compared to the developer time, and while we're getting "less for our money", because we only pay for the active time, it's actually cheaper for us than Jenkins was just for hardware rental, let alone developer time managing Jenkins.

I can completely see how a different org with different constraints, different deployments, clouds, strategies, provisioning, distribution of engineers, etc, could come to the conclusion that you did – that BYO is better, but I think it does depend on so much.