You are right there is no logic to this at all.
My mate asked for a couple of his similarly aged (65+) friends to be put on his policy for a long trip to France, and they gave him a reduction in premium! I can't fathom that one out.
My wife's mileage has been increasing recently due to her mother' nursing home being further away , so she phoned to report an increase in annual mileage to about 5000, and they quoted a lower number and gave her a rebate!