I don't think there is any way to change this (maybe apart from VBA). Most likely this is what Microsoft calls By Design.
And I guess it is meant to make room for the filter option. If you create a pivot table in a new worksheet and you apply a filter, that filter will appear in cell A1.

When creating a new pivot table you can of course check Existing worksheet and then in the Location field specify A1 (for instance) in a blank worksheet. However, if you now apply filter you will see that the pivot table is removed so that it starts in A3.