Even with cross-platform libraries, each platform is bound to have its own peculiarities and constraints. That means that each platform will require its own platform specific extensions, test setup and effort spent on testing and maintenance.I've never understood "if we get enough support we'll port it to Linux/MacOS/Android" or similar. There is no end to cross platform libraries to choose from.
Also, input devices and optimal resolutions are not equal when comparing a desktop PC with an Android phone or Android tablet. You can make a "quick port", but you can tell in advance that users will complain about that as well.
Don't get me wrong, I don't see why including Linux should triple the price either.