A steep drop just past the top
Prize money in tennis is heavily concentrated at the very top of tournament draws and the very top of the rankings, and it falls away sharply once a player is outside the small group that regularly appears at the largest events. A player ranked comfortably inside the top hundred can still earn considerably less across a full season than the gap in ranking might suggest, since most tournaments pay the majority of their total prize fund to just a handful of finishers.
Costs that do not scale down with ranking
Meanwhile, the costs of competing barely fall as ranking drops: flights, hotels, entry logistics and a coach's wages are largely fixed regardless of whether a player is winning or losing in the early rounds, and a player who exits a tournament in the first round has still paid nearly the full cost of attending it. This mismatch between falling income and stable costs is the defining financial fact of the sport below its most visible tier.
Who this quietly filters out
The practical effect is a filter that has little to do with tennis ability: players without outside financial support, whether from family, a federation or a sponsor, can be forced out of the sport by cost alone well before their playing ability has been fully tested against a large enough sample of matches. This economic reality rarely appears in match commentary, but it shapes who reaches the well-known tiers of the sport as much as any single technical or tactical factor discussed elsewhere.