Supply - demand
That is all you need to know. If the supply is less and demand remains the same, then the price increases. The value of a bitcoin is irrelevant just as the price of an ounce of gold does not matter. That's why people buy gold in amounts smaller than 1 oz. now that prices are high.
If demand continues to go up there may come a day when people say; "You own a whole bitcoin!!!"
How is the value of bitcoin or gold irrelevant? Of course the price matters. People wouldn't invest in something if they knew it was going to lose them money. Gold is more of a safer bet and will hold its value well but as an investment it's not that great, and that's where bitcoin can excell.