Sure, they can have multiple versions. However, having multiple versions means multiple designs and production lines and paperwork and regulation complience etc

Sure, they can have multiple versions. However, having multiple versions means multiple designs and production lines and paperwork and regulation complience etc. so Apple probably decided that it's not worth the investment. It's very unlikely that they were not able to, they could have done it the same we they did with other Apple devices that have a modem.