Koyeb also moved off Kubernetes and went with Nomad. We started with Kubernetes, thinking it was the right abstraction layer for us to build our platform, but then quickly ran into major limitations. The big ones: as others have mentioned in this thread, its complexity; security (we wanted to explore using Firecracker on Kubernetes, but it was very experimental at that time); we were not interested in keeping up with its release cycles; global and multi-zone deployments was not as straightforward as we needed; and the overhead (10-25% of RAM) was a cost we were not willing to take (we are around 100MB with our new architecture).
We wrote about our decision to switch here: https://www.koyeb.com/blog/the-koyeb-serverless-engine-from-...