Combination of these two honestly. There's a very sudden, catastrophic drop in viewership between seasons 6 and 7, where the average episode in season 6 pulled in 3.5 million viewers on average, while season 7 pulled in just barely above 7. Even though the internet was already having an impact on ratings (many popular cartoons in the pre-internet days would get viewership approaching 10 million or more), such a sudden implosion can't be explained by that alone, as there was no sudden technological shift that turned people away in an especially faster fashion than before.
Breezy was in Season 6, and I've seen a LOT of people say they dropped the show after that episode. I wonder if the public at large didn't follow suit.