Tend to agree too. I manage a fleet of heterogeneous development boards, many of which are on vendor-slightly customised versions of Ubuntu. Most of their apt repos point to cmake 3.10.
There are a couple that are outdated now, but I think it makes sense to go by minimum default on the oldest Ubuntu LTS, given its probably going to be the lowest common denominator. CMake fails clearly and quickly when the version is too old anyway.