We choose github actions because it was tied directly to github providing the best pull-request experience etc. We actually didn't really use github actions templating as we'd got our own stuff for that, so the only thing github actions actually had to do was start, run a few light jobs as the CI was technically run elsewhere and then report the final status.

When you've got many 100s of services managing these in actions yaml itself is no bueno. As you mentioned having the option to actually be able to run the CI/CD yourself is a must. Having to wait 5 minutes plus many commits just to test an action drains you very fast.

Granted we did end up making the CI so fast (~ 1 minute with dependency cache, ~4 minutes without), that we saw devs running their setup less and less on their personal workstations for development. Except when github actions went down... ;) We used Jenkins self-hosted before and it was far more stable, but a pain to maintain and understand.