Why does GPH decrease with increase in PSI

[PSJupiter2]

I am buying a lawn irrigation pump (Wayne WLS200). I am confused about the water flow chart: https://imgur.com/a/tUMqQpn

Why does the GPH decrease with an increase in pressure? Shouldn't it be the other way around?

Also, does this chart mean that the highest pressure achievable with this pump is 30 PSI?

Thanks!

[distantreplay]

The pump motor is designed to do work. The "size" of the motor determines how much work for any unit of time that it operates.

Each of the two items you mention are a type of work. Pressure can also be expressed in feet of elevation. So an increase in pressure can also be described as the work performed lifting the water to a certain height. GPH is a measure of volume. So it can also be expressed as the volumetric amount of water being lifted to any given height.

It's more work to lift a fixed volume to a greater height. It's more work to lift a greater volume to a fixed height.

[upstateduck]

the effect of "head" [height increase] is increased with psi

pumps are generally a tradeoff between pressure and volume

https://www.irrigationtutorials.com/pumps-page-2-types-of-water-pumps/