A third party library that uses the library from a non-standard repo has to then mention that repo in their build.gradle file also. Which used to not even be published in the pom (this may have changed). Whatever happens, that custom repo then needs to make it into the published pom. (Something at one time frowned upon if not outright denied in public repos… maybe this thinking has changed also… but the maven folks are super-dogmatic.)
So then this custom-repo stuff propagates out like a virus.
Then one day the auto-magic-publisher stuff decides to change the paths (because it’s not really meant for this… at least the jitpack-auto-magic-stuff isn’t) and breaks every one of those custom repo references that are forever in the public repos. (Probably why its frowned upon, eh?) “But they would never move the path…” Except they have at least once already.
So in general, if you want to publish your library to a public repo then it’s best to have that library only depend on other things in the public repos. Ergo, if JME is not in a standard public repo it’s essentially limiting the folks who would like to produce trouble-free libraries that depend on JME. As one of those people x10 or so, that would concern me.
There is also essentially no benefit in NOT publishing to public repos. The work has already been done to make that possible.