Why do dehumidifiers put the evap upstream of the condenser?

I should probably know this, but I honestly don't deal with dehumidification in my area near as much as most of you. Our summers tend to be very hot and dry from july to sept.

The few stand alone (big) dehus ive messed with lately have the evap first, and cycle the compressor to keep from freezing up. These are pricey units, and I don't understand the engineering.

• why do they run evap pressures low enough to freeze so quickly?

• why don't they run some or all of the condenser air through the evap first?

Im staring at a psychrometric chart and can't see what i'm missing.