What exactly constitutes content quality?

Artists with a rough touch or simple art style seem to be frequently rejected or ignored.
Why is this?
Is there a reason?
For example, what do you think of these?

post #11364469
post #57316812
post #57258527
post #57290647
post #11336256
post #11336407
post #11364260

You can ask for advice regarding post quality in topic #7934, additionally if you want to share things that haven't been posted yet, make sure you're sending the asset id and linking them like such: asset #48234141.
If you want an idea on what constitutes quality then you can look at approver:any to see posts that have been approved.