Is it because of their weak English skills? NO, its not because of their weak English skills, but its because of lack of practice.

So only one thing which helps in getting a better Writing score is nothing but PRACTICE: more and more of practice. But if you practice without evaluations, it is like shooting in the dark.

Now you can use IELTS Online Tests writing evaluation service which uses real examiners to give an estimated band score. There are 100s of written tasks to choose from.

Link: https://ieltsonlinetests.com/writing-evaluation-service

The detailed feedback and an estimate band score will be sent to you via email in 48 hours.