Because quality is better to be measured by the numbers, not the stars.
A newbie in the game, in the fist 1-2 seasons, doesn't understand the difference. He just looking at the stars 3-4-5, so, a 3* player with q 14, it's about the same with a 4* player with q 15 but managers are buying those 4* players.
After some seasons, the managers prefer to buy only players with q3/4 or q 8/9 because they understand that those players are closer to the next star. A player with 3*, q 10 with a 4* player, q19, have almost 2 stars difference, not 1.
Few more tips about that :
- The gaining of a player is dropping gradually when his is increasing his q. A 5* player with quality 39, is closer to a 6* player, q40 than a 5* player, q35
- When you checking an oppo, don't look only the stars but the quality of the players too. Just pass the mouse cursor over the stars and it shows you the quality (in pc version)
- Its easier to sell a player q9 or q4 and it may cause a small bidding war, so if you have a player lIke him and have some extra sp, count them before give them to him (he 'll be q0 or q5). Better waste them. Those are the most difficult to sell, players.