Patrick,
How can a club that is offering a pool, tennis, billiards, card room, etc. reasonably cut back? Sure, you save some by closing the pool and tennis court and turning the lights off in the card and billiards rooms, but you still paid for building that stuff, you still pay property taxes on the value of the larger clubhouse with all of these ancillary rooms.
Those bad decisions are with those clubs like a ball and chain around the ankles, while those that concentrated on golf, while they didn't benefit from the growth in the full service country clubs that occurred over the past few decades, will be the ones more likely to succeed in the future.
I'm sure it was easy to get started down the road, as guys who wanted to join a club found it easier to sell to their wives if it had a pool for the kids and a nice restaurant for her to lunch with her friends. Then when tennis started getting popular in the 70s it probably made sense to add tennis courts so that any decline in people golfing could be made up for by the growing tennis market. As members get older and not enough younger people join expanding your lessons offerings seems like a reasonable idea. If you want to increase year round business you need indoor activities for the winter, so you add the billiards and card rooms. A few members have their kid's weddings or receptions at the club, and you decide there's money to be made by putting in a big banquet room and offering it to the public. Maybe when smoking bans are instituted in the state you add a smoking room if there's an exemption for private clubs. At some point during all this (maybe more than once) the clubhouse has to be replaced or at least added to. It probably all makes sense at the time, but undoing it and going back to core golf is pretty much impossible, even if all the members were behind it.