- Privacy issues - Owning critical service component
Unfortunately I've never heard the reason that I think is the right one ( at least from what I can see is happening here ), which sounds like :
"Hey, we don't need this, because at Zalando / Nokia Maps, etc. we used Jenkins, so I don't wanna spend time maintaining a new tool ( CircleCI )."
Same stuff happens with project management ( dominated by JIRA around Berlin ).
At one point a company trashed all my CD-setup ( which was with the free plan anyway ) to run Jenkins with Docker ( I don't know how well supported docker is with CircleCI, but I doubt that is so much different than Jenkins ).
EDIT: I'm freelancing in Berlin, so I usually do a hand-over when the team of devs is hired.