Architecture and cost and time all play a part in the decision to play, but I do tend to think that the latter two are more important to most casual players than the first (although I understand that they are all related and there is some cause and effect there).
When you look ahead, however, it will have a lot to do with kids and how many of them take an interest. The time issue is clearly a big one, but there are other more subtle factors at work: the decline of caddy programs that introduce kids from all backgrounds to the game, the trend toward two working parents, safety and supervision concerns, etc. I learned the game from my Dad. He learned it because he caddied from the age of 9-14. Neither of his parents played nor paid for him to play, but access through a caddy program was all it took. That path is almost non-existent now. When I was a kid, my mom did not work and so it was not that hard to get a ride to the course in the summer. I certainly did not have as many activities as my kids have, but I also had a parent who had the time to take me. That is less and less normal now. I also would routinely ride my bike several miles to the course as young as 10 or 11. My wife and I would never let my 10 year old ride his bike that far. Granted, I grew up in a smaller town, but parents are less likely to let their kids roam off to a golf course by themselves than they used to be. There are many factors like that, which I notice more and more as my kids grow up and I try to steer them toward an interest in the game. Many of those shifts have good reasons, but they are what they are. The old days of a 10 year old kid from Pittsburgh (my father) riding his bike 6 miles to his caddy job all summer are gone and not coming back.
Another thing to consider is Tiger. This is either a positive or a scary negative, depending on how you look at it. Despite the challenges facing golf (and junior golf specifically), the sport is facing all of that at a time when the abolsute most famous athlete on the planet is a golfer. That is a very rare benefit. My kids think golf is cool and great in part because of Tiger. I may have been able to get them interested without him, but it sure would have been tougher. They even like to watch golf on TV (but only if he is playing). I sure didn't do that as a kid. It is scary (to me) to think of how much worse off the sport might be, without the interest that he has driven. He will not be around forever.