I often wonder if part of the problem is the lack of exposure to model kits today. When most of us were kids you could find models just about anywhere, drug stores, department stores, and let's not forget the many hobby shops that carried an extensive selection of kits. Now we struggle to find brick and mortar stores that carry them, and those that do, have a limited selection that doesn't always appeal to everyone including myself. I have heard Walmart and other big box stores don't carry them because they take up to much space and return little profit. I don't know if this is true, but a youngster looking through the toy department will never come across models and want to try one. Sure there are lots of online possibilities, but let's face it, when your young and want something, you want it now. Add on the cost of shipping along with the actual cost of the model I think there are far to many other interesting things kids and parents will be drawn to.
Hot Wheels still sell very well, so although I do agree many younger people are not interested in cars, there must be enough of them out there to sustain other car related products on the market.
I believe companies like R2, Revell, and even Moebius are producing models that attract us old folk because we buy them and will find them wherever we can. Attempts to make models of newer cars may not have sold as well as the older muscle cars. Just look at Revell's 68 Chevelle which has been so popular.
I don't think kids really care if the body is 100% accurate or the wheels are perfect. I know I didn't back then, it was just fun to open a box, and start gluing an painting.
Somehow the industry needs to get some exposure with kids beyond those of us who tried (in my case) to inspire our kids to the hobby. I could sell the worlds greatest whatumacallit, but if nobody knows its available I won't sell many.