That's because the Ravens have so many CBs in front of him. They had 11CBs at one point in camp. They've IRed two of them. They have Peters, Humphrey, Smith, Westry, and Stephens (2021 - 3rd pick) ahead of him. They also had 2 vets that he was battling with in Averrett and Young. Stephens wasn't exactly lighting it up for the Ravens, but he was their 3rd round pick.
Did you stop to think that maybe they realized that short of other injuries, there was no real way to keep Wade? That trading him was better than losing him to waivers? Or did you stop and think that maybe the Patriots reached out about Wade specifically and they weren't interested in Warrior, Young or Averrett, so the Ravens felt that the Pats offer was the best one available?