Choice of state variables in circuit theory
In traditional and present day linear circuit theory and analysis memristors are rarely if ever considered in any practical sense because the parameter \$M\$ that relates flux and charge is difficult by any passive means to physically realize. And I'm not sure that one could engineer say with op-amps a virtual memristor without the use of complex and expensive charge and flux sensors. The other parameters \$R\$,\$L\$ and \$C\$ on the other hand are easily engineered using passive materials.