This hits the nail on the head for Wonderland... Thanksgiving is the 2nd Monday in October... The demarcation line for the start of the 'Christmas Season' in Canada is the day after Remembrance Day. Play a carol before then and people lose their minds, but after November 11th, everyone shifts to Christmas mode...
That and the first year Wonderland did Winterfest it was way, way, way more popular than anyone expected, so after being shut down for May and June, they weren't going to miss the chance to make some extra money in November...