those were luxury apartments belonging to a huge retirement home owning multiple buildings within milano. the exact reason for the low fees isn't mentioned neither in the calcioefinanza article, nor in an other one i read. but in the article they are stating that the apartments should have been used to support the activity carried out by the organization pio albergo trivulzio (google them, there are plenty of info on them)
in hungary, similar cases usually revolve around corruption and tax evasion. those apartments are usually owned by the state, a budapest district or a state owned company. managers usually let buddies (friends, lovers, political allies) get the opportunity to rent these at low fees, who then either re-rent them for a profit, or simply live in them. so they are either part of a compensation package, or just a petty scheme to make money and damaging the owner (= usually the country or the local government) who could otherwise rent the place at a much higher price.
it's not unreasonable to suppose that if it's a retirement home, then there must be some old people who would have needed those apartments, and who didn't get access because the vip's occupied these apartments, and they did it while paying the fraction of the market price