The Mac version resumed development when the Kickstarter goal was met, but platform concurrency was not a stretch goal, and was never promised (even for Mac, Larian was unsure if it would catch up to the Windows version by release). The Linux version was always planned to be started once the OSX version was done; that was very, very wrongly expected to be not much extra work after the OSX version was done, but there was always going to be development time required.
People in general were predominantly supportive of the delays to the original release of the game, given the extra content being added and changes made. Anyone who backed the Kickstarter for the Linux version who was unhappy about the delays with that version could get a refund.
