I guess one reason is that PSB, DM and Duran Duran have all sold many times over the amount that The Smiths have. They have also reissued their classic albums many times in several different formats. So there's much more physical copies around that the fans can listen to. It also seems that for some reason The Smiths is a band that the youngsters (who very rarely buy records) seem very keen to investigate and some even become fans, who listen to them through streaming services over and over.