I think when Nickelodeon announced the hiatus of new episodes for Rugrats Nickelodeon never knew how Rugrats popularity would spread like wildfire and as you can tell based on the success of The Rugrats Movie in 1998 Nickelodeon thought Rugrats would be a one-hit wonder after the hype of Doug and Ren And Stimpy but the critics were wrong. I think why Rugrats got so popular that Nickelodeon stopped the hiatus and went ahead and more episodes of the show were made. But once Rugrats ended and they created the spin-off All Grown Up that show was an even bigger success for Nickelodeon and they wanted to expand the Rugrats franchise but it never happened