This is a lot of conjecture, but I would imagine they (and yes, radio stations in general all seem to have evolved to this similar format) are gunning to have their "big topics du jour" for when most people are listening. So in the morning drive, commuting hours are typically 7-9 for the majority of people. The changeover between shows typically is boring and sucks, so starting the show at 6 and allowing it to get rolling so it is in gear for when the commuters start leaving is ideal.
Ditto the lunchtime crowd, no one is taking lunch at 10 so waste that airtime for the people who would be listening regardless, and afternoon shows start at 2 so by the time the commute home starts, same deal. I could be way off but it works out well for four hour format shows to be staggered that way, as opposed to the morning starting 7-11 or 8-12, etc w the later shows falling where they do as well.
I will guarantee they have studied the numbers and they know PRECISELY what time they want what they consider their "money moment" to be.