Why, though? Let's say I'm making a game. Browsers web workers and WebGL. Why shouldn't I target that universal platform that will allow people to play on Macs,

Why, though? Let's say I'm making a game. Browsers web workers and WebGL. Why shouldn't I target that universal platform that will allow people to play on Macs, PCs, Linux and all major mobile platforms? It just seems very odd to draw lines in the sand that don't need to be there. How is any of it bad design or an "anti-pattern"?