I think “bringing younger people into the hobby” is definitely and issue.
Driving and owning a vehicle seems to be less of a “right of passage” as it used to be, but that is only a small part.
I think the year limitations and unwelcome attitude at car shows and cruises towards the import crowd, makes them feel unwanted and unwelcome. The limiting might be used as a method of controlling the size of some shows, but it also serves as a message of “you are not one of us and we don’t want you”.
Cost of owning a collector vehicle is very prohibitive to someone starting out.
The price of fuel also limits how much these cars get used and with a bad economy people often have to make choices where to spend their money, often a car that you can’t afford to drive or work on is an expense that can be done without.
Maybe another factor is the inability to work on your own car. We had simple engines an electrical systems. Now it is mostly electronically controlled and you need expensive tools to diagnose a problem. 30 years ago we could build a decent car for a few thousand, fix it for a few hundred and fuel it for 20 bucks. Now, you can’t touch a decent car for under 10 grand, it will cost you thousands to fix up, a hundred bucks a week to fuel, and then you need insurance…