Why does iPhone 5s have so many different models for GSM and CDMA netwrok? Very confused?
This is only a problem if you are buying the phone (unlocked) in another country from the one you want to use it in.

If you are buying the phone in the same country that you intend to use it, then all you have to do is see which model of phone is sold by the carrier with which you intend to use the phone, and then buy that same model.

If you are in a different country, ask someone to visit a shop in the country where you intend to use the phone, and check the models sold for your intended carrier.

I suspect that the real reason is not to somehow punish and confuse potential customers (they really don't want you to buy the wrong one, despite how it feels to you now), but is more to do with available chipsets for the various LTE bands.