That's what it was!! I have two Macs. My 2009 Mac Pro can only upgrade to El Capitan (OSX 10.11.6) but my MacBook Pro has High Sierra (OSX 10.13.6) and ESC opened up on the MBP! Thanks... don't know why I didn't think of that!?
*UPDATE: It works just fine on my 2009 Mac Pro too. Since I have them networked together in my music studio, I just dragged the ESC game into the applications folder on my Mac Pro (from the MBP) and it played without issue. The .dmg just wouldn't open on the older Mac...