The former Rangers player made 10 appearances for the Dons since joining in the summer after failing to make a first-team breakthrough at Bolton.
The 22-year-old asked to go out on loan but talks with McInnes on Wednesday ended with his contract being cancelled before he signed an 18-month deal in Paisley.
McInnes said: "Obviously we gave Gregg an opportunity to come and be part of something and we felt he had a part to play. He's probably not had the opportunities that he maybe anticipated but the team has been doing well.
"But that's only part of the reason. Players get an opportunity to show every day in training when they are with us that they can stake a claim as well.
"Gregg obviously feels he needs to go and play more regular. Obviously that hasn't been the case and I wasn't getting the impression that was going to change.
"We wish him well and we have no doubts he'll go and get regular football at St Mirren. He's not a bad lad at all. We were just looking for a wee bit more determination to fight his way into the team."