I hate to disappoint you, but the short answer is "nobody knows for sure." It's similar to the stock market. You can get a PhD in finance and/or economics and still not be able to know what the market will do. There are many times when a company will have only good financial information (positive cash flow, good operating income ratio, etc.) and yet their stock value will go down for no discernible or sensible reason.
Of course there are differences between the stock market and BTC. I'm just saying that they're similar in that they're unpredictable for the most part. BTC is much more volatile, and if you time it right, you can make money on the swings. That's if you time it right
The value is determined by what people are willing to pay, since BTC is market-based. It's as simple as that. The "why," as in why they are willing to pay that amount, is an entirely different and far more complex area.