Yeah there was a pretty big change to writers. And Groenig and one or two of the main guys (and who knows how many writers) were busy with Futurama starting in 99 (or maybe even prior to that).
I think even the format of the show changed, and its how a lot of other shows go, where they basically just try to stuff pop culture jokes/references in and focus less on the story and characters that the show built. So instead of building coherent storylines, its basically a sand box for them to use the characters to make jokes.
The thing is, I see people reference stuff from later seasons (like 8-12) when I see those people say it went to shit after like season 6 or 7. I think there's quite a bit that happened after people realize and that the show didn't go bad as quickly as commonly believed. And that people watched it longer than claimed.