If the league you involved in this season is tough, probably this is the reason that strikers score less. You should also consider the average score per match of the whole league when evaluating scorers.
On the other hand, in my experiences, many strikers are really not good at scoring even if they have good match ratings. Some of them have many assists. But others' contributions may even not be reflected in either scoring or assisting. If I have this type of striker in team, I will firstly consider the team performance. If it's good and scoring burden is carried by other strikers or even attacking midfielders, I will not rush to replace strikers. If team performance is bad and especially team scoring is also bad, I will not trust the good average match ratings of poor scoring strikers and try to replace them.
Anyway, after there are sufficient matches proving that strikers are not good at scoring, in most case it is permanent. If you really need a striker with more scoring contribution, you have to replace him.