it is easy and faster to choose the one who is known to be fair, not posting plagiarism and original content, some of the curators simply choose such users like in this example.

Again, it's the responsibility of the curators to find more authors. It requires more work and more time so some people just choose the known-ones, like you said.

I observed that many good authors don't follow clubs because there are less rewards going into the pocket for their hard work. Since clubs, so many authors have switched to voting services or have simply moved to HIVE.