There are chips that support all networks like Qualcomm's rf360. So the phone would have cost them $20 more to make but in return be useful to millions more customers. Their sales could have been 5 million instead of 500k.
They can't even produce 5 million. America isn't in their market plan right now. They will eventually come, but how long is it going to take them to build up enough clout to be seen as a good business decision by the carriers?
I know they've tried their best to separate themselves from OPPO as a company, but I'd be surprised if they had any more mainstream success in the states than OPPO has and for mostly the same reasons.