My guess is economical reasons:  1.  Being the simple (not to be construed as unintelligent.  There is a difference)  creatures we Americans were in the 1950s, we had a hard enough time just getting used to the features that Royal and all the other American made typewriters already offered.  Machines that had too many features were more intimidating, and were not as popular as one advertised as "Easy to Operate."  Ease of operation, a good touch, and good print were about all that were wanted in America back then;  2.  If things such as paper stands, half-spacing, and extra keys were offered, the machines would have been more expensive to buy.  How does it go, our grand old system of capitalism?  Oh yes!!  It's  Whatever the market will bear.  Royal and the others were geared more for selling as many of their machines as they possibly could, and to load them down with extra features would have added to their cost, and they couldn't sell as many.  If anyone wanted a typewriter with things such as half horizontal and vertical spacing, half-spacing, and paper rests, they could do either of two things:  1.  Have a Royal or any other American typewriter individually added with one or more of these options (I have a 1957 Royal electric typewriter with a half-backspace).  I've had an IBM Model A Executive typewriter with two extra keys--making it 88-characters.  Alot for IBM, but not quite up to the number usually offered by Olympia and other foreign typewriter makes;  2.  While we're on this subject, a buyer could then opt for an Olympia, Adler, Everest, or other fine foreign machines that did offer these options standard.  I think such typewriters are neat myself, and I love playing with the extra goodies from time to time.  

beak wrote:

What is certain is that Royal had their reasons - I'm just not sure what those reasons were.

Fully agree. The simplicity argument makes no sense given Royal portables at the time had some of those features such as paper rests. My guess is that American businesses didn't demand those extra features in their standards, and maybe a bit of perspective is needed. I can understand why a typewriter user in 2016 would appreciate and want features in a standard that make it an overall more versatile typewriter, but from the viewpoint of business users in the early '50s, especially those who employed pools of copy typists cranking out identical letters all day long, those extra features might have been viewed as unnecessary frills.