Dunne had a dreadful season, in fact, if you trace it back he was dreadful the tail end of last season too. Things seem to fall apart with Micah and Ned got injured within a couple of weeks of each other in Feb/Mar last year and since then it's been all downhill for Micah and Dunne. I'm guessing that Micah carried the injury into this season and as a result his form dipped, being young that can be hard to get back. Dunne getting close to 30 has no time, he can't sit on the bench for a season and then make it back into the first team, Richards can.