Why are some people in stackexchange more interested in editing questions posted by others rather than providing answers to questions. Are they just doing this for the rep?
Because questions which are posted by new users are not formatted properly. There are grammatical mistakes. Sometimes these questions don't have proper tags associated with them. Many contributors have their favorite tags in which they're specialized. If questions don't have proper tags then it might not let them know that there has been question raised. Thus it reduces the chances of questions getting answered properly.
Formatting questions properly makes more readable and it's easier to understand. And hence it increases it's chances to get answered quickly.
Also for new users who likes to contribute can edit questions. If these edited questions are approved by senior members (more than 2000 reputation) of community then it earns them 2 reputation for each question edited. Once they reached beyond 2k then they don't get 2 reputation for editing a question.
Rohit has really hit on the main reasons I would edit and not answer. There are a few tags in particular that are heavily abused by new users, especially anything with Salesforce in the tag name. For instance, many users will tag a post with
salesforce2salesforce because they are trying to let us know their question is about the Salesforce platform, but their question has nothing to do with this feature. A large number of my edits are in an attempt to buck this trend and keep those tags dedicated to the features they represent.
Dave's comment really encapsulates what should be conveyed here as well:
Just because you know how to ask a question well and try and help new users clarify what they are asking for doesn't mean that you know the answer to all the questions that can get asked here.
Many of us have spent enough time around here to know how to ask good questions that convey our problem clearly. Some of us are experienced enough with the platform to know how to answer a given question. The overlap between these two circles can be quite small on some questions.
Besides the reasoning for why someone would edit your post, you need to take a step back and realize that you are asking for people to volunteer their time to help you, probably with task you are being paid to perform. As such, your opinions expressed here in your question and comments are extremely entitled and do not show much appreciation for those efforts.
If they can understand the question well and can edit it, why can't they provide the solution too? Are they lazy enough to give the solution?
This view is reprehensible, and if that is how you see the community, you're never going to get very much out of it or put very much into it. Learn to appreciate the help others are trying to give. Edits are an attempt to help you get what you need.
I think the best way is to ask the questioner to elaborate the problem clearly with screenshots[if necessary]. Editing or down voting the question neither help the community nor the questioner because only the questioner will have the proper understanding of what's wrong with his code or functionality. If there is serious spelling mistakes and irrelevant tags added to the question that leads to misunderstanding of the problem then its ok to edit the question. Down voting can be given only to wrong answers and not to questions. Down voting a wrong answer may help the other people to not waste time with that answer.