The Atlantic says that Warren should run for the simple fact that she is the only thing that stands between the Democratic Party nominating Hillary Clinton in a landslide. It does seem as if Hillary Clinton does have a pretty easy and straightforward path to the nomination if Warren does not get in her way. Even with Warren in the race, Clinton could still win.
Democrats are a little concerned about putting forth a nominee that has not been battle tested against other candidates in any way. It would leave all of the attention on the Republican side of the nominating process, and this could be quite difficult for them to handle. Having that much media attention on one side of the political spectrum can sometimes shift public support to that side.
Warren has repeatedly denied that she is going to run for President, and if she sticks with those claims, then there may be no contest at all awaiting Clinton and her walk to the Democratic nomination.