16" wheels and tyres are by far the most popular size for 4x4 vehicles around the world - esp in third world countries, where it can sometimes be hard to get anything other than 7.50x16 tyres! Hence one reason they are popular for expedition vehicles.
I like them because they are taller; for the same amount of sidewall you get a 1" taller tyre. On the other hand, for the same overall height of tyre, I guess it's debatable if less sidewall is a disadvantage or a virtue. With an already tall tyre, 33" or larger, I personally think more sidewall becomes a distinct liability. Yes, more sidewall allows more flex, but if you air down a long way, huge sidewalls start to fold instead of flex. So I prefer 16", and could be persuaded that 17" or 18" is a good idea from a technical point of view.
More steel/alu and less rubber also makes for weight reduction on big tyres, and you're buying and discarding less rubber on each set of tyres.