Passengers are not meant to understand the complexities of network carrier pricing strategies. Making this transparent would be giving up a huge competitive advantage.
In addition to the points mentioned by others, you also have to consider the way that yield management systems work to optimise revenue for every seat. This means that at the time when a request comes in for a seat the system engages in a bid/offer process which looks at the point of sale, the value or cost of inbound/outbound connections to and from the primary longhaul segment, and other factors. It then has to evaluate whether it should release the seat/s or hold on to them in the hope of obtaining a higher yielding sale closer to the time of departure, or possibly ending up with an unsold seat.
The number of seats allocated to the various yield management 'buckets' (subclasses) are constantly updated according to complex and mysterious algorythms designed to baffle the customer!