The schedule has to go through a number of layers before it is approved. The Tech guys have to look to make sure they can deal with classes that jam up against each other where the Tech volunteers have to work on multiple classes. There is always a kick back from guys who run multiple races in different classes. This shows up in the polls that SCCA sends out. Then there are the racers who raced on Sunday last year and want Friday this year and those that raced on Friday that want Sunday......
Then, you take into account that this is all happening while the staff is negotiating for the following year's venue and they are launching the new Majors and Super Tour schedule, yada, yada, yada.
So, May Day is the best they could do.