Most Kickstarters for games now include or add support for Linux. I doubt most games would do it if not for HumbleBundle which requires Linux support and can earn you $100k to $300k or so. If not for HumbleBundle the number of new customers a Linux build gets you is almost certainly not worth it.

People still treat Kickstarter like a pre-order system, also Kickstarter disallows you from posting renderings instead of actual products (pretty much all game publishers do this).

That's only for physical products, you can still post rendering for games.