Unfortunately it's the game itself. In team sports for example you have regional sponsorships. So the 80th best player in the league can still make bank in a particular region. In tennis the only team concept is national attention but that only comes with big time success at the Slams. Mind you Australia does a far better job than Canada for example but that's not going to change universally any time soon. How the payouts work might be tweaked but there are still massive advantages the higher seeds get that translates into easy money. Plus not every tournament can have the prize money payouts like the USO which gave 58k for 1st round exits and 18k for 2nd Qualifying winner. Indian Wells gives 16k for 1st round losers as one of the higher secondary tournaments but when accounting for expenses that might be close to minimum for a lot of players. But to change the cultural thinking of giving more prize money to 1st and 2nd round losers is asking a lot. As for subsidies for tennis in poorer nations, that's unlikely to happen outside individual player involvement.
The easiest way or I suppose the most logical to predict future progression is considering previous periods of progression and multiplying by 2. For example, look at progress made in movies from 1980-2020 and consider that same level of progress will be made from 2020-2040. Same in sport. Reality of sport in North America being saturated is just, well undeniable. The money aspect stems from shift in sponsorships, not necessarily more people spending a higher percentage of their earnings. But let's look at gridiron football, in the 1970s a lot of players in the highest league (NFL) had second jobs during the off-season, if not more than half considering all the bench spots. Now a lot has improved but most contracts are not guaranteed and the average tenure of a pro is still about 3-4 years. We'll see how brain damage affects the future of the sport but there's already a noticeable trend in student athletes playing less football. I mean, brain damage for no money and higher risk of injury inherent to the sport.
But what do you think is realistic by 2050 for example? Surely the only captivating next thing would be a player winning all 4 Slams in a year right? Then what if it happens more than once a decade? And most of the records won't just be unreachable, the Top 3 in most categories will be unreachable.
