Because the value of a dollar fluctuates.

I've noticed that, just like when we just dropped from $280 to $260, the timing corresponds with an increase in the strength of the dollar. And in other times when the strength in the dollar decreases, the price of bitcoin goes up.

We have to recognize that we are measuring the value of bitcoin against a currency whose value fluctuates from time to time. If $1 buys you a loaf of bread today, and $5 buys you one loaf of bread tomorrow, then then it follows that 1 BTC will be worth more $$ tomorrow. I don't know why nobody talks about this.