The Batman: Arkham Knight PC port was bad. It was so bad, Warner Bros. stopped selling it for a time. It’s so bad, it still isn’t completely fixed about 8 months after its initial June 2015 release date and over three months after its October 2015 rerelease. Which is probably why Warner Bros. isn’t bringing it to Mac or Linux systems anymore.
Batman: Arkham Knight was supposed to be on all PC platforms, but Warner Bros. has finally confirmed that it won’t happen and suggested that people who pre-ordered the game for that reason should get a refund. Batman: Arkham Asylum and Arkham City both were available for both Windows and Macs. Given the state of Arkham Knight , however, maybe it’s for the best that the ports weren’t attempted.
Source: Steam