Well, that's quite wrong actually.
When ED was running on PC, XB and PS, the consoles combined were accounting for 15-25% of the player base and macs numbers were so low they got dropped really early during ED's shelf life.
So 75% of the platforms is meaningless since those platforms combined had less than 25% of the players, while maintaining the game on the said platforms apparently wasn't profitable, at least not to a level that would support future investments
Simple as that.
If the platform cannot support the game development, the game will not be further developed on that platform.
Wait! Isn't that exactly what happened with ED on Mac, XB and PS?