Multiplatform? Really? I'm thinking "Who cares?"
Linux is probably what you really mean. Mac is in its own world and most people are afraid of the BSDs.
Ok, Linux. Which Linux? Which version? Which steaming pile of GUI shells, window managers, and widget libraries?
I think the truth behind Linux is not the cost of Microsoft's OSs. Not anything supposedly crummy about Windows. No, I think people are just out of ideas of software to make, so moving to Linux lets them feel that they are doing something cool.
Know what? They aren't cool. An OS is an OS. That's it. Just the box of blocks you make something out of. And Windows still offers a nicer box of blocks.
So why build anything out of Linux's blocks? It's more work and nobody cares. Don't give me the mountain climbers' excuse: "because it's there." Cop out for sure. Dont be fooled, they're just out of cool programming ideas.
The preceding was a glob of half-baked opinion by one guy.