After long periods of hot weather, you can get very strong winds pick up with little warning.
It's one thing to make a marginal call for yourself in your well found boat, but as lead skipper, some of the boats and skippers would have been unknown to you.
Imagine the consequences if the conditions from your forecast did materialise and you had committed people into them.
By calling it off early, skippers could get together to make their own decisions as to whether they wished to proceed separately.
It's easy with hindsight to post "millpond" pictures but you had a tough call to make, and I think you did THE RIGHT THING with the information that you had at the time.
All the Best