Still in the race?

When I was browsing the internet today, I came across an article that was about the presidential race. It was about Hillary Clinton and her abilities to win the democratic candidacy. The headline read, "Why is this woman still smiling?" I was just wondering if any of you could answer this question. I am a supporter of Obama and think that she should just drop out now. The longer she stays in, the battle between the two of them, the longer this drags on. The article stated that his delegate count is rising, so why doesn't she just drop out? She obviously is not going to catch up in the month or so left of the country's primaries, so there is really no reason for her to be wasting her time and money. Hopefully she will soon come to her senses and realize there is no way she will catch up.