If the sport is your full time job you can't live unless someone pays you to do it.
How come nobody complains when some drug taking alcoholic rock star who's been banging underage girls manages to salt away multi million pound fortunes?
A lad I grew up with went on to be a top Rugby Union player
He was pretty much told he would be a shoe-in for the full Ireland team if he applied to be eligible - his Dad was born in Ireland
but he thought that was wrong as he is English
he was only kept out the of the full England team that won the World Cup by people like Martin Johnson - and a bias in the top ranks of selectors towards Southern clubs - he played in the North West which was a no-no (too much League!!!)
so he was a strict amateur
a concept of which ended because some players in the South were employed as Stock Brokers and the like - based on a hour a week in the office drinking tea and the rest of the week training (or so I heard from "people")
He was a copper and bent his training and playing around the shifts
mind you - his colleagues were very happy about an insanely fit 6 foot 6 second row being around when the estate pubs kicked off!!!
Oh and his Dad could have played at Wimbledon - but had a family to support so opened a jewellery business instead and Wimbledon was strictly amateur in those days as well
Things have changed - at least in some sports