The logic lies in a fare structure which tries to find the maximum price that the passenger is willing to pay for various features, including flexibility. Business travellers are prepared to pay more for flexibility because of why they're travelling.

So how do you identify them and make sure that the pony up the extra? By making the cheap tickets inflexible at precisely the time that the business traveller most wants flexibility - ie on the day of travel itself. That's the time when people are turning up early at airports because their meetings have gone short, or late when they've overrun. So they business traveller who doesn't want the risk of sitting around in the airport for many hours will pay extra for the ticket with the extra flexibility.

The leisure traveller, on the other hand, may have problems with their travel the month before, the week before, or even two or three days before - they've lost their job, the house has been broken into, the mother-in-law is sick, or whatever. They don't have an increasing need for flexibility the closer they get to flight time. So they will be more likely to be happy with the restriction, and be more prepared to pay the very lowest price they can find.

The real boon in these conditions is (IIRC) the move away from "travel or bust" conditions which are common for the cheapest tickets over here in Europe. No changes, no refunds. At any time. You fly on the flight you're booked on or you buy another ticket. Dead simple.