The defender had started all but one of Stanley's 21 games this season before the Gills clash, but was not even named on the bench at the weekend.
Richardson explained the 32-year-old needed a rest following a busy fixture schedule, but says he understands the frustrations of those left out of his team.
The Reds boss told the Lancashire Telegraph: "Peter doesn't deserve to not play. He's played a lot of games and I thought it would do the lad well to rest. That is the only reason Peter didn't play.
"He's been absolutely outstanding throughout the season, as have other lads who aren't playing and who aren't even getting a shirt at the minute.
"I do feel for them and if they stick with me and stick with us, all the better, because the lads need pushing and we need all the help we can get."