I am also a UW-Madison admit, and I was contacted by one of the faculty members two days ago. As the faculty who contacted me was one of the POIs that I named in my SOP, I think the department (maybe the DGS?) matches prospective students with faculties of similar research areas, and then the matched faculty contacts the admitted applicant individually. Thus, I wouldn't take the current situation as a 'lack of desirability' or anything of that sort just yet. Your assigned professor may just have been busy or lazy.