Lets see, Crosby gets Rust and Rakell, and when he was playing terrible they moved Geno up to his line to get Sid going.... Geno gets Bunting, Tomasino, O'Connor, and when he starts to play terrible, which coincided to being dropped back to line 2 with lesser teammates, they don't do anything, except talk about trading for slugs like hoglander and other reclamation projects to mix on his line.
Crosby is going to continue to get Rakell and Rust, Rust is very mediocre and lazy af, but is opportunistic so will get his points, the heavy lifting that Rakell is doing for the top 2 lines is pretty amazing, Crosby and Malkin play leagues better with Rakell on their line. the only linemates that Malkin has shown he can have decent results with, that does not include Rakell, is a small sample size of Glass, Malkin, Tomasino, and Tomasino will crash back to earth here soon, if it hasn't happened already. Bunting needs to play with a line of Bunting, Lizotte, ,Puljujarvi, and the forth line can just go away forever.
short answer is Coaching, this teams issue is coaching