Upvotes and downvotes are personal opinions. However, in almost all cases, many agree on one point and thus, you see more voting on either of those sides (up or down).
The question is not worthy to get upvote unless it is edited by some great people (some high rep users edited and made post more clearer).
Not true. Questions get upvotes if they are worthy, not who asked or edited them. Yes, editing play some role but then it is only to make the question clearer. At times, the original posters need support to put their concern in appropriate words. This has nothing to do with great people or users with high rep. I've seen and approved many new users who edit questions (including my questions!).
I suggested to edit the title because you clarified that your concern is to find polite or less severe version of 'none of your business'. The title with just 'Why for you' did not serve the purpose then.
Clear titles are important here because ELL is a highly reputed website cached by search engines in a very short period. It comes high on SERPs when you search for any English language question. Imagine these two cases:
The original question as it may appear on search engine result pages:
Why for you
I'm not sure googling which 'query' would bring that up.
And, after edit...
Softer, politer synonyms for 'It's none of your business'
This might show in results if people search for alternative, softer version, more polite way to say 'it's none of your business' or queries the like.
And, for this sake, why simply search engines; the new users do such searches on ELL as well (a local search).
Better title, easier search, great results!
So, as I see, there are two concerns of yours that I try to answer
a) editing is suggested/done in the interest of the community
b) editing a question does not ensure any 'shield' to downvoting. Editing just clarifies the question further with better words, formatting or sentence structure
About reasons of downvoting, why don't users leave comment after downvoting -they all have been always moot points here.
You may read J.R.'s answer here. You may find it helpful as a new user to this site.
I personally find this site for learners to make them pundit!