Most rental companies purchase, maintain, store, and insure hundreds of thousands of dollars in inventory. Some weeks much of this may be necessary, other weeks it is just overhead.
I have ONE modular PA system that can be scaled to suit larger or smaller events.
Also, I have meticulously assembled my sound system with efficiency in mind, in terms of output levels for its size and weight, and even in terms how much power it consumes to make a given intensity of sound.
The system in the photo above, suitable for engaged audiences up to fifteen hundred, can be set up by a single person in just a few hours, fits in a cargo van, and could operate at capacity with three 20 amp (2200 watt ) AC circuits.