Even though the NFL allows the Denver Broncos and all 31 other teams to carry 90 players on their roster throughout the course of the offseason, there are few NFL teams that would probably realistically keep that many guys on their team even if they could.
Reps are harder to come by the more players you have on the roster, and right now the NFL doesn't have a perfect system in place for developing younger or less experienced guys who maybe only have a short window to make an impression on an NFL coaching staff before entering a grueling workout circuit, provided their agents can get them tryouts throughout the season.