To throw my $0.02 in here...
I started and stopped MRR a number of times in the last few years, and reading this thread sort of strikes a chord with me. I am in the middle of the age group (I am not a new comer and not an old timer. I did have a 4x8 layout when I was very young in my fathers workshop, which is one of the main reasons I keep wanting to get back into MRR). I used to have a large space to put a new layout, but I do not have that now. Still, I have two observations to make about attracting new comers...
1) Money. Some comments point out that you can get into this "on the cheap". The problem is that searching for MRR on the net, you will find and see great, wonderful layouts, with DCC engines that make prototypical noises and lighting. These things are no where near cheap. A nice DCC engine with sound is how much? Those highly detailed cars, without weathering, are how much? Each one of those buildings costs what? How much was that single tree? A box of 25 pieces of track costs what? Each one of those turnouts were how much?!?
A lot of you would probably say "well, it took a long time to accumulate all of those items", which may be true, but we live in an instant gratification society. Someone wanting to play a computer game (as noted by another post) can spend $20 to $60 on a computer/console game, get it instantly, and play by themselves or perhaps with 10s, 100s or 1000s of others. They may or may not spend more money in the game, but typically over the life of a game it would not cost much more. I will not even delve into the free insane time distractions that are social media. Compare and contrast that in your mind with wanting to build a MRR (in my current situation, there are no MRR shops or clubs within a 250 mile radius of my location). I would have to build baseboard ($200 + how many hours?), order track and perhaps one engine, cars, controller, wire, solder, soldering iron, tools (oh, the cost of tools! Add up how much your tools cost that you use for your MRR) and get to work. Unless you really enjoy building, getting to "I can run trains around this thing" is a journey in and of itself.
2) Level of effort to get into the game. At one time I was planning a nice sized layout in the basement. Something happened during the design phase, and this is what caused my pause and eventual demise of the MRR journey: It was going to cost nearly a grand for the wood alone to build the baseboard. Not to mention the time and effort it would take before one could even lay down a single rail. Sure, I could start smaller, but again I go back to "look at these awesome layouts on the net". Thinking back to when I was young, I had a 4x8 on a pair of saw-horses. A beginner could start out that way, but I bet all of you can guess what happened the first time a friend bent over the middle of that 4x8 sheet to get a look, and leaned on it hard.
Baseboard is important, costly, and takes a great deal of time and skill. There are volumes of books on how to build the baseboard alone. Someone who wanted to get into this even with a 4x8 sheet is looking at real money. (are you going to go to the lumber yard with all of your dimensions and ask them to cut all of the wood for your baseboard (probably at $120 an hour), or are you going to go to the tool store and buy a mitre saw just for your baseboard?) I am sure we can all lay out perfectly logical excuses and solutions to this problem, but someone wanting to get into the game with no power tools, no truck and no shop has a large hill to climb before they can start a "real" layout. After all, setting it up on the floor is great for Christmas, but not as the beginning of your MRR empire.
While it might seem like I am going off on a negative rant, I will admit that there is a great deal of joy in MRR. There is something very satisfying about being able to say "I built that" and see the trains roll around your yards and mainline. One of the main issues is that the "youth" (and plenty of adults) today have a lot more competing for their time. Before 1994 one did not spend their time looking at the computer so much (if at all) and we certainly were not distracted constantly by the computer in our pocket we continue to call a "phone". I think getting more people interested in this hobby (IMHO) would be easier if we could figure out how to break down the high cost of entrance, and the high cost of work+money in the initial baseboard investment. It is a tough cookie to swallow if you want a "large" layout. (and having written those words, I realize I wanted a "large" layout)