There are, proportionately, a lot of 9-hole courses in the Manchester/Cheshire area of England. Some are long-established private clubs, others recent pay-and-play and the occasional municipal. They all seem to have found their right niche and don't seem to be in as much trouble as the private 18-hole clubs in the Manchester suburbs. Several are close to bankruptcy and a couple are to merge, selling one of their courses for development. They are losing those members who play only a few rounds a year, because green fees for, say, ten rounds at pretty well any standard of course will be considerably less than their annual sub. (Of course, there are very few private members' clubs in the UK that don't allow uninvited visitors). They might have a problem at one or two places because they don't have an active handicap, but there are some very good courses around here (such as Delamere Forest and Wilmslow) that do not require a visitor to be a member of another club nor to have a handicap.
Some private 9-hole clubs will not sell a 9-hole green fee to visitors. They presumably don't want many visitors. But several will do so and it presents an attractively short round for those in a hurry and, very likely, a better 9 holes (design and condition) than will be found at any of the pay-and-play or municipal facilities.
I know of only one 18-hole course (a municipal in Sandbach) which will sell a 9-hole green fee. It is so crowded that your nine holes may take 3 hours - you don't play there to save time!