Just cos I have Norks! (with a capital N
)
There is one style and brand of bra that I have ever found, that I can just buy "off the shelf" that I know will fit me -as long as I take the bloody instrument of torture wires out - but the damn thing is at least £40 :(
I have tried others over the years, but they just don't fit, even in supposedly bigger sizes 
I tend to have one really tatty one, one with no wires in that is on the road to being tatty, and one newish one for "best".
Last time I bought one I got lucky and found one in my size on eBay for £25, but today I had to fork out forty quid :( and to add insult to injury my new knickers were a ridiculous price as well 
£48 for six pairs of giant pants!
I give up, I am becoming a hippy and wandering the streets commando, with my Mighty Norks swinging free in the breeze round my knees from now on!