He got injured. He was on pace for 13 goals and 40 assists as a sophomore. That's not lighting the net on fire but his overall production was still solid.
Did anybody have any concerns about Galchenyuk's declining goal totals of 30-23(adjusted for injury) and 19? There has been so much emphasis on "trading a 30 goal scorer", whereas he only reached that plateau in one season and hasn't scored more than 20 in a single year.
I think we all had fantasies of him finally putting it all together becoming a #1 C and putting up a bunch of points but it seems that the reality seems to be that he is what he is, a capable yet inconsistent scorer. Somebody here made the comparison to Andrei Kostitsyn, and to me that's a great comparison. A player that possesses all of the tools but not the tool box to use them.
Here's a decent article for anyone that might still think about jumping off the ledge: