Don't see the issue

I agree that the system is fairly straightforward and is used in many parking places worldwide. They tried to introduce a similar system at The Bodega Aurrera where you paid at the checkout - but that was soon disbanded as nobody wanted to pay to shop. The big shopping mall in Acapulco has a similar system but the pay machines are actually in the car park.
The most notable thing to me, at the airport, was that when they had the pay-booth then you paid a minimum of 28 pesos for 2 hours - but now, with the new system, it is a minimum of 30 pesos for 1 hour - over twice as much!