I'll always prefer the feel of winter football to summer football, but that bolded point by CelticTiger is the most sensible I've seen in regards to this.
Bottom line is most clubs can't move to winter football because the grounds aren't up to scratch. The casual fan won't want to stand in the rain at a ground that is partially covered. Couple that with how cold certain grounds are during the summer and you can only imagine what they'd be like in weather like this (I genuinely believe that being an away fan in Morton Stadium in December would lead to hypothermia).