The NFL is a pass-first league, with offenses designed to gain chunks of yards through the air. The league likes the scoring and the highlights that come with pass-happy offensive systems, and teams have evolved into spread systems with three, four, five receiving options in routes. The additional receivers on the field has led to limited formations that include multiple running backs on the field. That limitation has turned the fullback position into a relic in the eyes of many, though there is plenty of evidence that a fullback can open up an offense.
Serving as an additional blocked in pass protection, a chcekdown option for the quarterback, or a lead blocker in a running play, the fullback can still be a key member of the offense.