What the linked article shows is an image from the developer Robotality for their 2014 strategy game Halfway, showing Linux at 2% sales/Mac at 4% with support requests for Linux at 30%/Mac at 50%. Sales around that mark for Linux are quite normal, any developer expecting more must have done no research. I would like to point out that Robotality themselves do continue to support Linux, with Pathway releasing in April this year.