That's because of the general perception that .com domains bring in more eyeballs than others.
To a certain extent that's true, because ignorant users or user knowing only your site's name but not the TLD (.in,.com,.net etc.) would try .com first as it's most common/popular.
What you ought to do is get both sitename.in and sitename.com and have the .com redirect to the .in
After which you should promote your site everywhere as sitename.in and not sitename.com
THat'll make users & prospective new users link your site with sitename.in instead of .com