A new steam update was just released, with a note for Mac OS that said "Fixed crash in some newer games when launched from Steam." I wonder if that will solve your issue? I'm not sure why nobody else would be seeing the issue, but still.
Incidentally, did you try running the game directly from the folder it is installed in, rather than from within Steam? That would tell you right there if Steam is the problem; if our game is crashing without being launched from Steam, then something is up with the interaction between our game and your computer in some fashion, and Steam is blameless. But if it crashes when launched from Steam and not when launched directly, then that's probably a Steam thing.