It’s not just elite private prep schools that aren’t ranking students. Most high schools in the United States as a whole no longer rank students. Among the minority of high schools that do rank students, some make submitting rank to colleges optional. The percentage of high schools submitting rank is even lower than overall national average among HSs in higher SES districts, which are common among Ivy applicants and posters on this forum.
If you look at non-elite public colleges in most states (not all states), which get few “elite private prep high school students”, a large portion of students still do not submit rank. The first ones that I searched for are below. I chose publics in northeast states that get a lot of Ivy enrolls.
SUNY Albany – 22% submitted class rank
UMass Amherst – 33% submitted class rank
Rutgers – 42% submitted class rank
Regardless of whether the OP’s high school is in the minority that submits rank, his top 1% ranking is fine for Ivies.