I used to help out in my mother's menswear store. Something that I learned was That the most common size was around 97/38/xl in trousers and shorts, so she stocked the most of them. This meant that there was good choice for everyone in that range and they always found something they liked. This customer is less picky than the smaller customer.
The smallest size 30,32/82/S was a tiny market comparatively, and there was only reason to stock a small number, or often none. The small customer would come in, be unimpressed with the much smaller selection than other sizes, not find anything he liked and leave with some smart remark. We are then stuck with a few items that aren't being bought and are staying on the rack getting old. Without the gift of telepathy as to what styles to order in the small sizes in advance, it's not viable to offer that customer the same range as higher volumes.
For every 1 small sold, I'd say 3 went on heavy reduction sales often 70% disc. Our smalls didn't break even. We generally say if you really want it, order it and we will get it for you. They still don't.
What i'm suggesting is that perhaps the elusive manual transmission customer is a little/ lot the same? Stock a manual, and the customer walks away as he didn't have the yard option of colour, or seats, nav, etc.