But the GSM markets Apple has yet entered is larger than the CDMA markets and it is more cost efficient for apple to go after existing markets.
First, that ignores the reasons why other manufacturer make CDMA models, which is to get more sales and to build brand loyalty.
More importantly, actual sales tell a different story. Outside of a handful of wealthier countries, iPhone uptake has been very low, with many countries clocking in at under 1% of a carrier's customers buying an iPhone... compared to well over 10% in the USA (more like 16% by sales if we count upgrades).
The reason is, it doesn't matter if there are even a billion people living in a GSM country, if they can't afford to buy the iPhone or pay a monthly data contract. An example I give is India, where 110 million users of one carrier were offered iPhones. Under 60,000 were sold (0.04% uptake) because of the cost compared to people's low income.
So the huge GSM world market that people claim is left to be entered, seems a myth when it comes to expensive smartphones. CDMA sales would eclipse them easily.
The USA is still the largest iPhone market (45% of world sales) , and by sticking with ATT so far, Apple has made it available to only about 1/3 of potential customers here.
Imagine if the iPhone were available on every US carrier. US sales could easily double or more, becoming 2/3 of world sales. Apple would love it. Of course, it could take a while to do so now, since many people are either locked into, or happy with, Android handsets.