From what has been written by World Champions from the past, there has never been a large financial gain directly from the FIM, most of the rewards come in the form of sponsorships.
Due to the level of FIM funding, the qualification rounds are not supported by the GP riders as it would prove,for them, to costly to ride. IMO that is more reason to use riders that are prepared to earn their place by the qualification rounds to achieve their ambitions, than ones that wait for hand outs.