Because their funding comes exclusively from their clients, private rehabs such as GreeneStone tend to be much more flexible in their rules than those funded by OHIP or churches/charities (beggars can't be choosers). At my NA home group I ran into someone who was at GS with Ford, and he confirmed this; he told me that GS has a "great program" but attendance at lectures, groups etc. is entirely voluntary. This, of course, is the exact opposite of what Ford needs. BTW I also heard that Ford checked out CAMH and Homewood before settling on GS -- no surprise there, as those rehabs are definitely stricter (especially Homewood).
Also, regarding that "great program" comment: I think it's pretty obvious that Ford's need for people to take photos of him is a manifestation of his addiction, and I would think that any good rehab would see, and challenge, that. As for visiting bars (even if not drinking)? At Homewood that was grounds for discharge.
Fun fact: A patient I'm working with was at GS some years ago. Back then it costs $50,000 for a 55 day program.