Many generally demonstrate that the application of price on Y-axis and quantity on X-axis are regarded as a conventional application and sometime, referred to as an improbable approach in market forces of demand and supply, even though there are valid reasons in economics and business applications. These reasons are theoretically accepted and implemented in economic processes. The derivation of demand curve from utility theory and the cost of production theory (for supply) are needed to be compromised with the theory of firm. The price determination (as a dependent variable) for a product in the theory of firm is based on quantity of the product as an independent variable. Economic processes and theories have critically handled quantity measures on X-axis without complicating the theories of demand and supply (cost of production). Hence, the placement of price and quantity respectively on Y and X axes is definitely not a disorder. Rather, it contains valid reasons in economics beyond questions.
Senthilnathan, Samithamby, The Application of Price on Y-Axis and Volume on X-Axis in Demand and Supply Analyses
– Is it a Muddle? (November 23, 2009). Available at SSRN: http://ssrn.com/abstract=1511962 or http://dx.doi.org/10.2139/ssrn.1511962