As others have said due to the ages of most of these games and the lack of source code and the like so there is no chance of really building a new port, well you could try to do so through reverse engineering but that is just too time consuming and such, so older titles either use a standalone version of Boxer or ScummVM since most were either made before MAC(such as Ultima's 1-5), never had a MAC version made or their MAC versions are so old that there is no chance they would work on Mac OS X,newer games such as Witcher and the like usually have dedicated mac versions.