Ages ago the profession of Caddie was a low-paying job for people, who came from such poor backgrounds that their families couldn't afford to send them to school. They were uneducated and largely unskilled to do anything else. In places without a golf course they were likely unemployed. Their only career path was to turn Pro, which wasn't exactly very prestigious either.
This situation has changed drastically in the last 100 years or so and it keeps on changing. Today some of the finest young people look to caddying to advance their non-golfing career and at the other end of the spectrum you have the highly skilled Pro Caddies, who are making tens of thousands and sometimes millions. And in-between those youngsters and veterans there are the regular Joes, who want to at least buy a small house and provide for their family. Today Caddie is a job like many others, not the most high paying one, but you would expect it to be at least at the level of greenkeeper or administrative staff of the course.
The only problem is that five greenkeepers or one Pro Shop attendant can cater to hundreds of golfers during the course of a day, while a caddie can cater to one or (double-bagging, two rounds) perhaps four on one day. It is therefore obvious that Caddies must be extremely expensive, if they are expected to not sleep in the equipment shack like in the 19th century, but lead a normal life like a staff member.
To me it seems that due to those unfavorable economics they are a dying profession except on the very highest levels. Perhaps like a butler or housekeeper, who used to live and eat in the house and thus could afford to earn very little. Who has a butler anymore? Perhaps the Queen of England and I suspect her butler makes more than most of us.
Ulrich