How to handle Co-author who is not listening the suggestions to improve the paper quality
In every scientific paper that I have been involved in, there has been opportunity for co-authors to directly edit the manuscript themselves, if they wish to make a contribution.  If you feel that you have suggestions that are not being taken up, I would advise you to ask something like:


  Would you mind if I did a pass on the paper to edit in some of the suggestions I've made?


If your co-author hasn't been editing in your suggestions because they are unclear, overloaded, or not able to do so, this will give you a chance to adjust the paper in the ways that you want.  If, on the other hand, they actually disagree with your suggestions, then they may not want you to edit them in, and you can then actually have a discussion about whether and why the proposed edits should occur.

In short: I believe that you need to shift from being a passive critic to being an active contributor who provides actual text that accomplishes what you want to have accomplished.