Too many overweight women to cater for. Take Clare for instance, it would probably cost a fortune to tailor a garment for her - big bust, short legs, broad across the beam, so it wouldn't be cost effective.
However, there is ONE adjustment that would make the world of difference to the 'look' of a garment, and that is the length of the sleeve. The number of times I cringe when I see even celebrities who can afford the best, wear a jacket/dress/top where the sleeve is far too long. It makes the whole image look slovenly and ill fitting. In particular tailored garments should be wrist length. It doesn't cost much to have them altered, and I've had many a jacket adjusted on the sleeve.
As for men - just check out the likes of Frank Sinatra in a tuxedo - perfect sleeve length with a hint of shirt showing at the wrist.