In the initial implementation package names were literally mapped to a path with the equivalent of subst(".", "/").

So in that sense the java package names are based on the hierarchy of a filesystem.

Also, the method name goes to the right of the class name, so the only reasonable way to have a hierarchical name that reads in a single direction is to put the most general qualifier on the left and the most specific on the right:

com.mydomain.mypackage.MyClass.staticMethod()

well, for the same reasons the urls _should_ be the other way around, plus avoiding inconsistencies with other languages I guess (don't know what languages supported dot-named packages at that time, but I don't think they were the first ones)