They survive in the US almost entirely where they’re mandated and not because they’re wanted.
I suspect that this is mostly true as there probably aren't enough members at each club with a strong caddie tradition which would support a viable program without the requirement. With the exception of one club which wouldn't have me as a member anyways, I would never consider a course which requires caddies or riding carts. But if hiring a caddie is your thing, all the more power to you.
"When in Rome", as another poster noted, is key. I recently had a miscommunication with the pro shop at a course and had an "optional" caddie waiting for me in the afternoon. His chances of getting another bag were 50/50 at best so off we went. Nice young guy, marginally helpful beyond carrying my clubs, and $120 later, he seemed happy and I didn't miss a meal.
Unlike Michael, I once had a caddie at Spanish Bay who insisted on switching things out of my SwiftX into his single-strap bag and somehow my Samsung 2-generation old phone never made it when he switched things back. The caddie said I must have left it at the Inn or in the car- impossible since I had to take a call in the pro shop while taking care of fees and then went directly to my bag and the caddie. A resort-wide search for the missing phone over three days went for naught. Not a good thing losing your smartphone, even for a Ludite like me. Lesson: refuse to switch bags or supervise the process closely.
Unlike others, I've had only a handful of caddies in my many years of playing golf who I thought were excellent in their work. Most recently I had a caddie who never once offered to clean my ball and didn't make any effort to help the other players and their caddie look for lost balls. Total fees for his services came to just under $150 and he seemed annoyed that I asked him to carry my clubs an extra 50 yards to my car instead of leaving them at the bag drop.
The best caddie I ever had was also on the Monterey Peninsula. He was in his early 40s, an excellent player and an obvious student of human behavior. He was great in every aspect of his profession, providing just the right amount of information, positive without being overly-solicitous and verbose.
His manner and way of communicating demonstrated abilities considerably greater than those required for his work, so I asked him how he came to caddying and how long had he been doing it. He replied that he went to college for a year or so and thought he would try something different for a while and make some money before continuing his education. Time crept up on him and more than 20 years later, he still liked working outside, the money was great, and he got to play golf all over the peninsula including CPC, PB, MPCC, etc. He did say that things might have to change as he was becoming pretty serious with a girl who might want a different lifestyle. All of us liked him so much that we tried to hire him for the rest of the trip. He gave us his card, but he was booked through our time there.
Lee Trevino said that the reason there are so few minority players in professional golf today in comparison to when he was on the Tour is the decline of caddie programs. And though he didn't go into it, economics have a lot to do with it. At many clubs with mandatory caddie policies, the prices are set so that the opportunity costs make carrying bags attractive. I suspect that the percentage of golfers willing to pay $50 for someone to carry a bag is multiples of that at $100-$150. In the absence of kids making $30/bag plus tip for five hours, we have adults of all ages hoping to earn $100-$200 each day, most of it in cash and untaxable. If golf was indeed a "free market", I think that Bernie is right.