Others might be aware of more complexity, but at minimum, not all oneworld flights are codeshared by other oneworld carriers, and of those that are, higher-earning codes might not be among them. For example, flights from LHR tend to be available with lots of codeshares. Flights from OSL less so, flights from KTM much less so. In addition, in my experience airlines tend to be very restrictive in allowing codeshares, while TAs tend to be more open. So, an airline might allow booking an AY code on a BA flight LAX-LHR, but not a QF flight SIN-BNE.