It is absolutely possible to design those bikes, but in order to strengthen the frame you're going to have to use heavier materials and components. So then to

It is absolutely possible to design those bikes, but in order to strengthen the frame you're going to have to use heavier materials and components. So then to support a person that's double the weight, your bikes are all now also double the weight. And anyone within the average range who wanted to use a bike to pop around town is now having to put in some real effort to pedal hard on a heavy bike.