Rugrats is an interesting show to rewatch as an adult.
When I was a kid I thought the adults' B plots were boring but now that I'm older I empathize with the parents' perspective more.
It was originally for the parents watching the show with their kids at the time it aired, but it also seems like they made a show that required their target audience to age before being able to appreciate it completely.

As for the OP: it simply fell out of style. Rugrats clearly fits the 90s with it's rough animation style and gross out humor, but the clean thick-outline style of the 2000s holds up better today.