Maybe they are collecting enough data about you that they don't feel the need to bother you. Are you signed in to Facebook in your primary browser? Do you have the mobile app running in the background?

Since I've signed out of Facebook on my PC and kill the mobile Facebook app while not using it, I tend to get multiple push notifications per day, most of them asking if I know some random person.

My girlfriend, who is on Facebook daily, has never seen any of these notifications.