Here are a couple of options to try to understand why people think that way. I know because of this post I will probably be accused national traitor against my country by patriots again but... meh...
Option A:
1. Play Promods
2. Delete Promods
3. Play YKS map
4. Delete YKS map
5. Play Promods again
6. If you noticed the quality difference then congratulations. If not, try Option B.
Option B:
1. Play Tregion Map
2. Delete Tregion Map
3. Play YKS map
4. Delete YKS map
5. Play Tregion Map again
6. If you noticed the quality difference then congratulations. If not, try Option C.
Option C:
1. Play SCS Germany Rebuilding
2. Delete SCS Germany Rebuilding
3. Play YKS map
4. Delete YKS map
5. Play SCS Germany Rebuilding again
6. If you noticed the quality difference then congratulations. If not, try Option D.
Option D:
1. Play Rusmap
2. Delete Rusmap
3. Play YKS map
4. Delete YKS map
5. Play Rusmap again
6. If you noticed the quality difference then congratulations. If not, try Option E.
Option E:
1. Play SCS Baltic, Italy, France and Scandinavia DLCs
2. Delete SCS Baltic, Italy, France and Scandinavia DLCs
3. Play YKS map
4. Delete YKS map
5. Play SCS Baltic, Italy, France and Scandinavia DLCs
6. If you noticed the quality difference then congratulations. If not and you still like YKS map, then enjoy it with your life.