As such, my analysis shows the price should be below zero, because that's what should happen when the price goes down or sideways a lot. And yet the price defies these realities.
The price does not defy reality, your analysis is wrong. Bitcoin's price appreciates overtime and has been doing so since it first got traded. Except you're looking at a period of time after an ATH the price always appreciates in value when you soon out of the chart.
A currency which only goes down or sideways in value will be run to zero. One which grew from $0 to $70k is definitely up in value most of the time.
Bitcoin may not be highly possible to end up with zero value.