Well, one reason is that more people are now aware of btc and every single day there are people who are deciding to join the trend. And let's not forget the upcoming fork which is the segwit2x. This fork is more serious and better than the last one (btg). More investors are buying in to get more b2x as much as they can which adds to the surge of btc. Just when I thought we'll settle at 6k before the year ends, and now we're at 7k. Amazing!
I think things are going to change a little bit now that there is not going to be a fork, I think we are going to see a slight decrease in price now that the fork was canceled but even then I still think that the price of bitcoin is going to stay above 6000 and I think the price is going to recover before the end of the year.
Either way the price will correct. Be it with the fork (which i read is still on) or no fork. This price rise is not sustainable.
Let's just hope it don't crashes back to 3000 USD or so. But find solace in the 5000 USD region.