Wayne isn't scheduled to take part in OTAs because he's still working his way back from the torn ACL. Moncrief is in Los Angeles at the NFLPA's Rookie Premiere event. Landry is absent because he prefers to work out on his own in the offseason. He did the same thing last offseason.
It's not mandatory for players to attend the OTAs, but it's a little surprising Landry decided not attend. You obviously don't have to worry about him being in shape because he lives in the weight room during the offseason and during the season. It's more about developing continuity at safety with Delano Howell, the frontrunner for the starting spot. There's a significant difference going from Antoine Bethea, a proven veteran, to Howell, who has limited starting experience. And it's not like Landry had an impressive first season with the Colts.
But again, OTAs aren't mandatory for the players. It would just be good if Landry attended as the Colts try to improve a defense that finished 2oth overall last season.