The Avos were not Mechuyav to keep any Mitzvos of the future. Although it was something they liked to do, they didn’t forgo the needs of the time for a Mitzva of the future.
The Ramban says they only kept the Mitzvos while in Eretz Yisroel. The Maharal says they only kept Mitzvos Asei.
They do seem to have a different status, since when we reference the four Imahos, we are talking about Sarah, Rivka, Rochel and Leah. They were Tzidkanios but obviously a different status.