Why is Rack Mounted Step-Up Transformer Not Industry Standard?
I can think of no technical reason why one would be more difficult than the other. In fact, you could probably operate those transformers in reverse, except that the switches and maybe fuses would be wrong (and the approvals would, of course, be scuppered by such a modification). 

I can think of many reasons why it might not be desirable from a business point of view. The market might not be there, different approvals might apply, and so on.