This is a pretty well-known effect in gamedev. The specific numbers change, but Linux sales are only a small percentage of total, while generating much more development and support work.
At least dev work can be drastically simplified with middleware like Unity, which is how small studios can even consider Linux. But support difficulties are real. Players have so many possible distros, configurations, and drivers - actually supporting all of them would require a level of Linux expertise that gamedevs simply don't have (being typically Windows or OSX based themselves). Limiting yourself to something like Ubuntu LTS helps a bit, but there are still plenty of gotchas.
So it becomes a simple matter of numbers: given relatively small amount of extra sales, is it worth the extra work, and spending the time to learn Linux development and administration in sufficient depth? Sadly usually it is not.
Unity does not do your customer service for you. Also, bug fixes might only go into a future release of Unity (months out) and updating to the new release to get the bug fixes might break your game. Unity games that spend a few years in development often ship on a very old version of Unity.
At least dev work can be drastically simplified with middleware like Unity, which is how small studios can even consider Linux. But support difficulties are real. Players have so many possible distros, configurations, and drivers - actually supporting all of them would require a level of Linux expertise that gamedevs simply don't have (being typically Windows or OSX based themselves). Limiting yourself to something like Ubuntu LTS helps a bit, but there are still plenty of gotchas.
So it becomes a simple matter of numbers: given relatively small amount of extra sales, is it worth the extra work, and spending the time to learn Linux development and administration in sufficient depth? Sadly usually it is not.