Despite their preponderance of crazy niche models these days, the bulk of Mini sales have long been comprised mostly of the Cooper and Countryman. So with an all-new on sale now, you'd think sales numbers would be great, but they're far from it.

Car sales figures guru that Mini sales were down a surprising 20.5 percent year-over-year for September. For an automaker that just re-launched its core car, and a car that's a big deal for the BMW Group, that means something is definitely amiss.

The immediate reaction to this is that maybe buyers aren't warming up to the new Cooper (aka Hardtop or Hatch depending on where you live in the world) because it grew in size compared to the car it replaced. But when did you ever know Americans to turn down a larger vehicle?

No, the problem seems to be supply. A quick search of Cars.com this morning yielded just under 1,100 new Coopers nationwide available for sale. That's not a lot at all.

I asked Mini what the deal is and here's what they told me:

MINI remains a desirable and very popular car here in the U.S. but our most popular model, the MINI Hardtop, has been in very short supply this year because of the model changeover that started in the Spring. The good news is as of October 1st, three out of the four 2015 MINI Hardtop 2 door models, the Cooper with manual transmission, the Cooper with automatic transmission, and the Cooper S with manual transmission, have been released for retail sales and deliveries. We are currently sending the new models to our waiting customers and to our dealers.

So the issue seems to be supply indeed. The new Cooper launched as a 2014 model, but the 2015s came soon after, and they seem to be held up pending fuel economy certification. This means that buyers who want the new Coopers are having a hard time getting them.

It looks like this is about to change, which is probably about to help cure a lot of headaches over at Mini. I don't see why this car wouldn't sell well — yeah, it's bigger than it was, but it's still small, very fun to drive, and probably the best Cooper ever made in terms of overall fit-and-finish.

I guess we'll find out what America really thinks of them soon.