The downfall of the metal heroes was the identity crisis it suffered with the '90s programs. Shows like Winspector were just so odd, they barely even seemed like metal hero shows.
Also, a few of the directors who are working on the Kamen Rider shows now were just starting their careers (usually in the second unit) with the '90s metal heroes. For example, Hidenori Ishida was assistant director on Winspector, eventually going on to direct episodes for B-Fighter and B-Fighter Kabuto; Ishida was chief director of Blade and Kabuto, and those two are really reminiscent of the '90s metal heroes, IMO. I think that's what plays the biggest part in new Rider shows seeming so metal hero like.