I think it should have gone to Bianca.
As Kevin has said above, Mark is just doing something that many others are already doing, many of which with far more experience than he has.
Personally, I think the decision probably came down to Lord Sugar's own ego. Mark's business whether it's successful or a failure will likely just disappear into anonymity. Bianca's business on the other hand is going to attach women's hosiery to Sugar's name and probably has the fear in him that people are going to make jokes about it, especially if it turned into a massive failure.