It is too late to change the style. TOR wants to continue using Sweet because, no matter how horrible, WOT books (in North America, at least) are instantly recognisable. General Fans, who might not keep up to date with the series would know instantly that a new WOT book is out if they see it in the bookstore. They bring a sense of continuity to the series. No one who has read the wheel of time will be put off by the covers because they have endured them for so long.

As has been said, supposedly this kind of style was actually considered good in the early 90's. TOR has said it will issue new editions with different covers later, after all the books have been published.