The different JDK builds are almost all built from OpenJDK. Maven and Gradle cover nearly all use cases. The complexity is not that high.
With the DotNet SDK for comparisons sake, there is but one provider, and package management is provided as first class citizen in the compiler CLI, removing the need to even pick a "gradle" or "maven" style build tool in the first place for almost any project.
Checking a new developer has actually managed to install the correct JDK for a given project is still a thing I have to do, all the time.
Sdkmans docs also have no bearing on the multiple build systems in the java world too, which again simply a non-issue in DotNet and many others.