Not the OP and unsure of exact market - but I'm going to hazard a guess that "not to scale" is because of the needs of the design industry.

I suspect that this is the sort of thing that they print and put on walls so that the designers and developers can go wild with their designs and redesigns of wireframes for the product.

So if its on a wall, you really want it to be much much larger than actual size so you can see it from 5 or 10 feet away.

This is my guess anyway based on how I've seen product design teams work. Would be good for the OP to clarify as well.