I'm honestly surprised that more democrats aren't running anyway. Is there a mentality of "Well we don't stand a chance against Hillary, so we won't bother"? I really don't understand how US politics works :P
The campaign is in slow-mode right now. Right near the ending of this year and the beginning of 2016 is when the political season ramps up. The media will begin tearing into whatever they get paid to report. As for why people don't think they can stand up to Hillary, it's because she's a household name. We've been seeing her face on screens and in print for a very long time. This gives her a huge advantage. I hadn't heard of Sanders until the beginning of this year.
The Democrats have five nominees at the moment. The other three haven't really been making headlines. They may get fleshed out a bit as the campaigns run onward or they may just kind of hang in the background if they don't get much buzz. So first we have the primaries where if you're registered to a party you get to vote to decide who we'll try to run, and then we've got the general election.
Oh, really? Man, there you go. Very little about US politics makes the news in Australia at the best of times unless it's something pretty important. I've really only been keeping up with Sanders because my ex is from Oregon and she's in love with him haha.