Brown joined the Lions after being claimed off waivers back in April after he was released by the Buffalo Bills. In addition to the Bills, Brown previously played for the Washington Redskins and San Francisco 49ers, and he was always really viewed as a long shot to make Detroit's 53-man roster.
It's unclear why exactly the Lions decided to waive Brown right now. No signings or waiver claims involving them were included in the NFL's Friday transactions report, meaning that they currently have 89 players. Perhaps they will add somebody next week, but in any case, it's not like they're lacking depth at defensive end. They have Ziggy Ansah, Jason Jones, Devin Taylor, Darryl Tapp, George Johnson and draft pick Larry Webster, and there will likely be only four or five spots on the 53-man roster at the defensive end position.