I mean there are technical legal issues in the size of a class. For example, any member of a class can object to any settlement agreement or any multiple groups of class members can object to a settlement making managing approval difficult.

The flip side to Amazons argument though is that if the judge decided the class was too big they could break into multiple classes and Amazon would end up defending themselves on multiple fronts. Usually companies facing these things want to roll it all into a single class for that reason alone.