To be fair, most bike shops carry f*ck all stock.
Why more bike shops aren't like this I dont know. Size isn't an excuse.
Cos it costs a FORTUNE. Have you any idea how many different "standards" and options there are out there? Consider something like seatposts - most people want one for about £20 while a few folk will want a Thomson/RaceFace etc for £70-100 or so.
ALL the different models in ALL sizes, in ALL the lengths and ALL the colour options - that's thousands of ££ of stock which will probably not sell, it'll take up loads of space and look a mess. Same with BB's, 5 different "standards" in all possible axle and shell widths, cranks in every common length and colour, bikes in every single size along with sometimes 2 colour options and (for road bikes) often a triple or compact option as well as the normal 39/53 setup. It's just not possible and as an aside to that, NO memeber of staff in ANY shop can possibly know everything about all the stock.
It's just not economically viable to stock all sizes of all stock all the time.