Fully agree with the reasons Adi listed for falling realized prices.
On top of that, I would challenge your ingoing assumption "...reasons why revenue per unit falls (i.e. prices)":
Revenue per unit can fall even if prices remain stable, if a client aggregates data to a high level, there might be a mix shift involved: High-price SKUs are in decline and low-price SKUs are on the rise. That means that on an overall level revenue per unit drops, although prices for each SKU remain stable (or can even increase year on year). This is an often seen phenomenon in interview cases.
Fully agree with the reasons Adi listed for falling realized prices.
On top of that, I would challenge your ingoing assumption "...reasons why revenue per unit falls (i.e. prices)":
Revenue per unit can fall even if prices remain stable, if a client aggregates data to a high level, there might be a mix shift involved: High-price SKUs are in decline and low-price SKUs are on the rise. That means that on an overall level revenue per unit drops, although prices for each SKU remain stable (or can even increase year on year). This is an often seen phenomenon in interview cases.