That is a question I asked myself a short while ago. The reason is very straightforward. Although the two powers are devolved, as the hon. Gentleman rightly points out, changing the rules surrounding them and on whether or not they can happen on the same day is a reserved power. As that is a reserved power, it makes sense to keep any potential combination of elections as a reserved power for the
time being, as the two powers match up. Were it to be within the competence of the Scottish Parliament to vary that, it would make sense for the Scottish Government to have the power to adjust the combination rules. As it is, the two match up closely.