How much of that is due to U19 and the long awaited Enhancement pass shiny wearing off, and how much the time of year?
90 days ago was July, which is summer in the US. Server populations always have noticeable shifts at certain times of the year, e.g. summer, around Dec for the holidays and so forth.
How is traffic compared to 365 and 730 days ago? That's likely more interesting than 90 days.