OP here. This really got off topic. I guess the answer would be by carrying two SKUs where one (CDMA) is more expensive than the GSM modem model, Apple can lower their variable costs by only requisitioning CDMA modems upon request rather than putting them in all the handsets. That's pretty cheap.
Given how complicated the wireless industry is (SIM cards, LTE bands, frequencies, countries, carriers, locked/unlocked, subsidies, etc.) Apple, known for their simplicity, should be doing more. They should make one (1) handset that works in any country, any network, etc. A true global phone with all protocols/radios included in it. The variable cost goes up, but this is offset by having less SKUs to inventory (remember years ago when Apple had so few SKUs?) Also, charging $1149 a pop for the iPhone X, I don't think they're going broke any time soon.
Also, I wouldn't be surprised if the telecom lobby has a hand here. Verizon and AT&T (CDMA and GSM, respectively) have an incentive for there to be differentiation among the handsets to keep you from being able to easily switch networks.
Crony capitalism.