To answer the original question, why won't ALL Alfas sell?
Let's be candid.
They're a nightmare, bought by enthusiasts, endured and suffered by enthusiasts and only sold on to enthusiasts. They are difficult to sell, residuals are rubbish, maintenence costly, build quality questionable, mechanichally unreliable, not to mention the terrible dealer network, but us Numpties still keep going back.
I've witnessed non enthusiasts buy them to try something different or not go with the Golf/Focus crowd and most of them part ex them back in very quickly. A colleague purchased a top of the line Mito, in his ten months of ownership it was in the garage more than on his drive, he got fed up and chopped it in for a Mercedes A Class, a year on he's never looked back, but reminds me on a daily basis how rubbish Alfa are...............
I think this answers the original question?