Why Is It So Hard For Game Developers To Compile A Game For PC and Mac and Linux
I mean if OpenGL (available for all of the three OSes) is used all around the system and C++ is used as the game engine it should be very easy to compile for all of it yet %90 percent of the games are compiled only for Windows.

But I can see that even Rockstar (GTA 3 is now on the Mac App Store) and Valve (Source Games like CSS are now compatible with Macs) started compiling for Mac because everybody is buying a MacBook Pro nowadays and the market share of Mac is now %15 percent.
Why Is It So Hard For Game Developers To Compile A Game For PC and Mac and Linux
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I mean if OpenGL (available for all of the three OSes) is used all around the system and C++ is used as the game engine it should be very easy to compile for all of it yet %90 percent of the games are compiled only for Windows.

But I can see that even Rockstar (GTA 3 is now on the Mac App Store) and Valve (Source Games like CSS are now compatible with Macs) started compiling for Mac because everybody is buying a MacBook Pro nowadays and the market share of Mac is now %15 percent.