Part of what makes newsworthiness is the degree to which something is surprising or unexpected. Trump says crazy things all the time, so if there’s a debate where he says a few crazy things and Hillary says none, then that’s expected and not particularly newsworthy. The media can tend to report on things that are the most novel, rather than the most important.
There is a lot of bigotry and xenophobia coming from the Trump camp. That could be why it wasn’t received that harshly. If she had said that about Romney’s supporters, the media backlash would’ve been worse. But Trump has run a campaign designed to stoke racial and class resentments.
With Romney’s 47% remark, it was misleading. A lot of those 47% are senior citizens (who tend to lean republican) and active duty military personnel. Plus that was just a reference to federal income taxes, and poor people pay a bunch of other taxes other than the federal income tax. So hte fact that what Romney said was disingenuous (claiming that those 47% pay no taxes when they do, and claiming they all support the democrats which they do not).
Point being, Romney’s insult was inaccurate (a lot of those 47% voted for him) and Clinton had a point.