It's a mystery, though I have a number of theories.
1. There are simply a lot of furies, and being furry in and of itself is not enough to keep someone from earning money. This means that some furies are bound to have lots of money, and because visibility in the furry world is in large part based on how much art you commission (if you do not create art yourself) the richest ones are the most visible.
2. There is a kind of person who has just the right amount of autism to be both sucked into furry and also do well in tech.
3. People who are poor or working class don't have a lot of time or energy to spend on furry stuff, meaning they are filtered from joining or participating much in the fandom. This means that the fandom selects for middle and upper class people who have time, energy, and money to blow on it. So people with money are over-represented in the fandom.
4. Due to the presence of so many loud, insane, maladjusted furries, it's notable to see ones that aren't so insane as to disqualify them from a high-paying job. So we think we see more wealthy furries but really they are per-capita the same as or less than other fandoms.
5. There are many furies who really, really want art that caters to their specific tastes. So, they are willing to pay for it even when at their current level of earnings that money would be more productively spent elsewhere. They make enough money and are smart enough to budget so they don't ever need to publicly beg or anything, and this gives the appearance that they make more than they do.
6. They sold their soul to the devil. Without a soul they become a bisexual furry, but in return the devil rewards them with $300,000 a year.
7. Some combination of the above.