Why should a paper be reviewed by more than ten reviewers? One of our recent submission has been suggested to be revised by a journal (CS). However, we could not at first believe that we have to address the comments or points raised by 11 reviewers plus the editor's comments. The comments are very diverse and conflicting.

Is it quite difficult to address all the comments and satisfy all the reviewers. Everyone is a human being, even us.

How and why should a paper be reviewed by so many reviewers? Now we are not in a situation to withdraw the paper and probably it is quite difficult to address all the comments because of computational issues.

For the how question, I have this possible answer: Yes, the editor might have sent reviewer invitation to more than required number of reviewers; and to the surprise, all accepted it.
11 reviewers seems excessive to me too, but that is the situation you are in now so you need to find a way to deal with it. My starting point would be that it is the editor that makes the final decision not the reviewers, so it is her or him you need to convince not all 11 reviewers. Sometimes the editor gives hints one what (s)he thinks the main comments are. In that case you know what to focus on. 

If that is not the case you just have to make reasonable decisions and justify them. So if there are conflicting comments you need to show that you have taken them seriously and made a reasonable choice on how to handle that. If all the suggestions are too much, i.e. it would result in a book rather than a article, then the editor (and the reviewers) can see that as well. Just mention that and justify the choices you make.