If those bugs are only present in the Linux port, then yeah, Linux users cost more to support. But if a significant amount of these bugs affect all platforms, then you could argue that a Linux user is much more valuable to them than a non-Linux user because they provide better feedback. Assuming they actually care about fixing their product.

Part of the problem is that Linux isn't really one platform, it's 10 different ones of varying popularity (e.g. supporting Gnome on Debian with Wayland doesn't mean that KDE on Nix with X will work). And it costs somewhere in that 1-10x range to support it because of that.