Valve Software co-founder Gabe Newell in a chat with gaming news site called Kikizo explained that he thinks Apple "has never taken gaming seriously" and the company "can't even follow through [sic] on any of their commitments [to] game developers"
Kikizo: People keep asking you about a potential Macintosh version, and your stance is that this is a strictly Windows project...?
Gabe: Well, we tried to have a conversation with Apple for several years, and they never seemed to... well, we have this pattern with Apple, where we meet with them, people there go "wow, gaming is incredibly important, we should do something with gaming". And then we'll say, "OK, here are three things you could do to make that better", and then they say OK, and then we never see them again. And then a year later, a new group of people show up, who apparently have no idea that the last group of people were there, and never follow though on anything. So, they seem to think that they want to do gaming, but there's never any follow through on any of the things they say they're going to do. That makes it hard to be excited about doing games for their platforms.
Kikizo: So you think it's all because of staff turnaround in their gaming department?
Gabe: I just don't think they've ever taken gaming seriously. And none of the things developers ask them to do are done. And as a result, there's no gaming market there to speak of. We'd love it if they would get serious about it. But they never have, and can't even follow trough on any of their commitments for game developers.