ASOS is hardly a generic high street store. It loads hundreds of new products on every day. Some of those products are 'normal' (ugh), some of them are not.
Besides, men in heels are not necessarily cross dressing. Believe it or not, some men just really like fashion and putting together different looks and styles. Why should they have to go to some overly expensive specialist website to do so?
Also it would have taken you about five seconds to look at other shoes on the site and see that they rarely, if ever, include the model's head in these shots.