Why does the art change so much!!!Its reallg hard on eyes

"It's actually quite natural not just on Chinese Manhuas. If the artist can't cope up or just can't do it anymore, they would change them. Other than that, they still have a contract obliged so might as well say it also depends on their contracts."
Quoted from Deuiche on the manhua "Special Agent K" because I can't explain it any better.
http://www.mangago.me/home/mangatopic/3696667/

I really didnt know...Thanks for the explanation...