I honestly don't have any experience with linux cnc. A lot of what forms my opinion is the controller's marketability. Many controllers do not ship with a PC, which is a great selling point on one hand, but a limiting factor on the other hand. If a controller came with, or just was itself, a dedicated host, and is the only supported host, then linux is definitely a viable option that doesn't create any barriers to entry. But if a company is simply building a controller, and requiring the customer to provide a PC, I see it as a no brainer business decision that the PC runs windows, and not linux.