Why are the episodes shown out of order on Nick?
Precisely, because they wanted to. Nick US chose to show the episodes in random order, mostly, just for kicks, but sometimes, for special marathons or promotions surrounding a particular character or subject. Most kids won’t know the difference, but Rugrats purists do care, as it ruins the continuity. Yes, most of the episodes are self-contained, but the scheduling of episodes is key — for example, you know something’s wrong when Cooking With Susie is scheduled before Meet The Carmichaels, or if Dil We Meet Again is scheduled before The Family Tree. Most other Rugrats broadcasters, including foreign Nicks, Telemundo, AFRTS, YTV and Vrak.TV, show the episodes in production order.