The whole pricing structure for the railways is wrong, first class really would be better these days as a supplement to the standard class fare where the difference everybody pays is the same regardless of whether they're on a dirt cheap AP or something which reflects the true cost of the journey.
Why? It's market driven. Clearly a business traveller arriving at London in the morning peak is prepared to pay a higher premium than an off-peak leisure traveller.
A standard price either undercharges people prepared to pay more, or prevents "upselling" when capacity is available to do so.