The fundamental point is that they are more expensive because people are willing to pay more money, the real question is 'why are people in the US prepared to pay more for their golf'.
Having played extensively in the US, and a member of a club in the UK the following spring to mind:
1. Presentation is far more important in the US, and this seeps down through everyhting, people are prepared to pay (and to be able to be seen to pay) to belong to a course that can claim a big name architect, a x0,0000 feet clubhouse, a humidor, etc. etc. Little consideration appears to be given to the playability of the course or the enjoyment derived from playing, most enjoyment seems to be derived from being seen to be playing.
2. Golf in the UK is not cool, and doesn't have the same marketability that it does in the US. Therefore pros and people in the golf industry are not paid as much, new courses do not generate as much interest and claiming to be a golfer at a private course does not carry the same cachet. General interest in the game (with the exception of small pockets of Ireland and Scotland) is much lower than general interest in the US.
3. Corporate UK (whatever that might be), has not embraced golf in the same way that Corporate US has. I work for an American company, 100 employees in the UK and two of us play golf. In the US headquarters all top management play golf and pay to play golf. Sponsorships in the UK tend to be local (Sid the plumbers) in both nature and funding.
4. Land in the UK is cheap for golf (although land in general is expensive) for a couple of reasons, one is that the courses have been there so long that the price of the land that they are based on fails to matter (as previously mentioned), but the second is the common agricultural policy. A very large percentage of the new golf courses that I am aware of in the UK are based on farmland, in Europe farmers are actually given subsidies to turn land use to things other than farming because of the food mountain. In addition they can get extra funds for things like planting a certain number of trees and I believe (although I do not know for certian) providing recreational facilities.
The course I belong to had around 550 members and charges about £500 a year (joining fees were around £1000). This is, I feel reasonabl value for what we get. It may not be Augusta conditions, the green staff is limited, but at around £10 per round for the year, it's cheaper than paying to play per round, which along with playing in club competitions is surely the objective.
Dickie