You are only looking for the stars.
Have you noticed the price of the players in the market?

Some 3 stars can cost more that the 5 stars, like real life, the players that cost more, play better and also train better.

Probably your 5 stars strikers, are low cost, so they simple do not score.

Other thing that sometimes happen is If you have 1 very good player or 2 (5*) and the rest of the Team are only 3*, the good one simple play bad, and have always bad notes.