I think it's because most of the things on display there you could actually order, or commission. It's a trade show for a trade that says: yes, come to us, and we can do this. Unlike concept cars made by big carmakers for conventional motor shows, most what's on display at SEMA is there because they can do it, or because they have done it: not a preview of what somebody might do in a few years, maybe, only not quite like this, obviously.
Making show cars you'll never be able to buy is a practice that Elon Musk, founder of Tesla, once described as "so lame", and although the rest of the motor industry might reply that they're rather better than Tesla at delivering cars they do say they'll make, I understand where he's coming from.
Some OEM car companies now reveal concepts at SEMA, but, still, it feels like a small part, an aside, to the main event, which is dynamic, relevant, personal, and topical: here's what we can do for you, right now. It might be my new favourite car show.