Multi-OS software

Shouldn't the storage capacity of DVDs allow for software to be released for multiple OSs, like Win/Mac/Linux, rather than having to occupy their own shelf in another box?  Like movie audio, all the needed data is there, but the user chooses to select which language.  You could use the same data/resource files and have an OS specific executable for the user's OS.    

How can companies make 3 times the profit by selling 1/3 of its product to the majority of consumers and 2/3 to a minority of OS users who rarely purchase retail software?  Why wouldn't putting 3/3 in one package save costs on loss of profit from having to cater to Mac users?