I believe we expect moving to the cloud to be more expensive than running our own DCs as you suggest, but I don't believe that takes into account any 'wasted developer time' you might factor into this.
I believe we started building this platform when AWS was very new, and hadn't seen a compelling reason to transition from it to the cloud until now. There's a couple of posts with more details behind our decision to go to GCP, but primarily it was to leverage their data tooling.
Would be good to hear their perspective on this.