When your most common linemates are Lucic and Lewis at 5v5, you aren't getting a lot of great passes. A lot of gritty play, just not a lot of quiet space to get a shot from. When he was on the top unit, the play was between Gaudreau, Lindy and Tkachuk. If it works, no need to go elsewhere. Besides, when Monahan was in the slot, his textbook shot wasn't there yet.
It's going to take some trial and error to find the right fit for him now. Can't really use him on the top line, except for the odd shift. There would always be some chemistry with Johnny and Lindy. But we really lack secondary playmakers. Mange and Toffoli are more finishers.