Why would pay be meritocratic?
It doesn't make much sense, at a basic level supply and demand comes in - if there is a shortage of people with knowledge of the language 'wibble' then the market rate for them goes up... suddenly wibble developers earn more than wobble developers even if they work as hard as each other
then there are the effects of trade unions, professions etc.. which have a sort of protectionist effect... if tube drivers weren't unionised and applications completely open then there would be plenty of people willing to do the job for fewer holidays and say a 15k pay cut.