Well, or you ask yourself, from the business pt of view, why would they sell it in the US market?
Nikon tried with their J1/2/etc line, and look at how much market share they have gotten with that. I'm sure that factored in Canon's decision.
The USA market has always been "BIGGER IS BETTER!" and very resistant to change. Therefore, your average big electronic store consumers (remember, those are the EOS-M's target audience) pretty much look at those smaller cameras as weaklings. Combined with the Rebels (and Nikon's Dxxxx's) selling for pretty cheap, they would pretty much get those by default. Just look at the penetration of m3/4 and mirrorless cameras in the USA market in general compared to the rest of the world. Sure it has been growing, but for now still nowhere near the regular SLR lines.
Introducing another product here is quite very expensive. So your math becomes, which do I make more profits? Putting lots of marketing money in something that the consumers here are not screamingly demanding for, or keep selling only the line that the demand is still pretty strong? The EOS-M lens lineup is at the moment very weak. You're going to have a tough time convincing people to get that while at the same time bragging about the EF lens lineup that you can use with the cheap Rebel. No, that converter is not going to help unless they give it out for free (which still defeats the purpose of having a small camera).