Air Transat is a charter carrier, meaning that they don't operate on the same kind of sked as the Big 6 airlines and aren't bound by the same rules. Likely no other charter is allowing people to cancel either, and unless it was physically impossible for the plane to fly I'd be really surprised if they'd allow it at all.
The Big 6 airlines will impose cancellation policies (normally) for cancellations, but for charters generally it's no changes, no cancellations, period.