The players that compete in each of the majors does not vary that widely. The most points come from the higher tiered tournaments and to get into the higher tie

The players that compete in each of the majors does not vary that widely. The most points come from the higher tiered tournaments and to get into the higher tiered tournaments, a player has to have a higher amount of points, which grants the player direct entry, which is how most players get into tournaments. The only alternatives to get into tournaments are entry by wildcard or qualification via a qualification tournament, each of which only grants entry to a small minority of players in any given tournament. For the US Open, the top 101 ATP ranking spots are given direct entry. As I mentioned, ranking spots are largely self-reinforcing, so the entries do not vary considerably. Also, players outside the top 100 are not spending $20k per month to tour. That is a wildly inaccurate even for most players inside the top 100.