Changing the date of county conventions

Hello all - What would it take to change the date of the county conventions so that they do not conflict with Earth Day every year?

I know it will be impossible to make everyone happy and avoid conflicts but I would think that the environmental party would not want to conflict with Earth Day every year.

Is there a reason why it is always this day or is it a case of this is what we did last year so it would be good to do the same thing this year?