One of the downsides about playing in the NFL is job stability. One season you can be star, and the next you could be fighting on the fringes of the 53-man roster.
At the start of the offseason, teams are allowed to have up to 90 players on their roster, but only 53 of those 90 players will get a spot on the official roster come Week 1 of the season. That means 37 players need to be cut before Week 1.
This happens every year. Talented players with a lot of potential who get released before the season even starts.