You need developers familiar with the strange non portable mess called Objective C. You can write most of the game in C++, but if you want to keep it portable (and you really want to), you cannot really take advantage of any of the "good" features of Mac OS/iOS.
And you need to use Apple's IDE Xcode. The latest version is the most messy IDE I have seen in a long long time, designed by a lunatic with window fobia, and coded by a bunch of inbred monkeys (judging from its frequent crashes, horrible performance and barely working debuggers). The first somewhat advanced "text editor" with recommended specs of 8GB RAM and SSD for somewhat enjoyable experience (until memory leaks catch up even with that amount of memory).
And so on an on. Apple support for developers is miles behind Microsoft, it will take them years...if ever, to catch up.
To put it simply, the best thing about modern Macs is that you can run Windows on them.