This to me is 99% of the issue. It seems most US states have purposely made it difficult if not impossible for people to find places to ride. Also the penalties for "illegal" riding have increased dramatically. They have truly "criminalized" off road riding in the states which is probably most manufacturers biggest single market.
I know in NJ the fines are OFF THE CHARTS, along with losing your bike to impounding and severe criminal charges (criminal trespassing, felony eluding). They really throw the book at you these days.
I had a small dirt bike growing up and I was lucky if my dad gave me extra gas to run it, let alone take me to a dedicated off road park (also they did not exist at the time). As long as we rode in the woods and stayed off the streets, the cops did not bother us and if they did catch us on the street they just brought us back to our parents house. Unfortunately, my parents got frustrated the few times it happened and sold my dirt bike and never bought one for me again until I could afford my own.
Fast forward to 2015. My buddy a couple years ago was riding in the woods when they saw a cop in the distance. They kept going not thinking anything of it, when they came out of the woods the cop cornered them and gave them FELONY evading tickets. They paid $10k in legal fees and are now considered convicted felons for off road riding. How crazy is that?? It will follow them for the rest of their lives for doing nothing more than trying to blow off some steam on a dirt bike.
Along with the legal responsibilities (someone else getting hurt on your kids bike), there are just too many major liabilities out there for most people to consider the sport other than those who are diehard riders.
Our society is turning into a police state.