Following parameters can be considered (not exhaustive list):
Completion of a Research Cycle - the researcher has gone through one round of research cycle e.g. from idea / problem inception to publishing an article / clear his or her post-graduate research degree. This can motivate him / her to research & write more articles based on the research skill that s/he has acquired.
Published an Article Recently - when the researcher has successfully published his or her article recently, this can motivate him or her to embark on next new research / article writing.
Good Writing Experience with Others - when the researcher has gone through very positive experience / exposure with other co-researchers / co-authors, s/he will continue to collaborate with them in writing / publishing other articles.
The researcher Self-discovers s/he has the Passion to Write - self explanatory.
Academic Promotion Motivation - some academic researchers in some universities deeply influenced by this adage "publish or perish". Hence there is motivation to enjoy in writing & publishing.
No work in this world can interest you, unless you find the much needed pleasure in doing it. Nevertheless, pleasure is the only and ultimate reward one can get for ones work done..........
I'd like to ask you, How do feel or what is the percentage ratio that will given to your article when repeated writing it multiple times? and what quality that you will reach after these repetition(s)?
Yes, few years ago, I feel very painful in writing, but after I read no less than 1,000 articles , then, I am enjoying doing it, especially in English .
Beside this , I am really appreciating those English novels ,and I am enjoying reading it, this what I should have done 50 years ago . But no now.
I totally agree with Ramesh. I discovered since I found pleasure in writing, it becomes easier to write. However, knowing my strong points and capitalising on them while writing, has really helped too.