[ShockerCon]

Like KRM said, they didn't have any stock footage to keep it going. The only way they could continue it was if they adapted either an older show, or went absolutely insane and tried to adapt ZO and or J(they're Kamen Rider movies that are only 45 minutes or so long FYI). If Masked Rider managed to be popular enough, then they could have possibly pulled a "Zyu 2"(click here for info: http://powerrangers.wikia.com/wiki/Zyu2 ) and make new footage, which could have possibly even reignited the Kamen Rider franchise. But alas, Masked Rider flopped, fell into obscurity, and the creator of Kamen Rider swore on his deathbed to never let someone adapt his works again(or so I hear).