MASON and ECJ long predate the existence of Maven and thus were not designed with Maven in mind. Because some people have asked us to provide Maven support, we have done so, but, mostly thanks to Covid, our well of Maven maintainers has run dry.
Maven is surprisingly difficult and problematic to maintain at the back-end; and neither I, nor my students, nor anyone at GMU as far as I know, use it for MASON on the front-end. This makes it very tough to maintain, and I am considering discontinuing support for it and just relying on jar files, which are simple and easily distributed.
I would like to know who in the existing mailing list use Maven, either for MASON or elsewhere, and would prefer that it be retained. Speak up!