I have similar observation.
In the past, ST, AMR and AML in my teams shared scoring duties. Season average ratings of these players are usually 7.5 or above. Since about last 2 or 3 seasons, only AMR and AML can keep good form. In my 2 teams, no striker had average rating above 7.3 except one ST/AMR player of my level 20 team. At the same time, the average ratings of MC or GK increase in this period. I believe that there was a program change when the new matching "10" was introduced.
I am lucky that I heavily relied on AMR and AML to score and still feel fine without good strikers.
Edit:
My teams have slight strategic changes in last few seasons and are more defensive mind than before. Probably these affect performances of strikers. But this cannot explain why strikers still cannot score many goals in high scoring matches.