Belt Vs Direct Drive

HighPressure

The main reason for belt driving a pump is simple...you can run a lower RPM pump, which in turn will always outlast a 3400 rpm direct drive. Number 2 reason: because of the RPM in a direct drive...the pump can't pull from a non pressurized tank fast enough, most of the cheap units also have cheap unloaders. Look at your 3000 psi pump size...a direct drive will always have a smaller pump because at the higher rpm it can be built smaller...and "cheaper".
I currently run one of two units...a fifty thousand dollar Putzmeister 7250 Psi 230 degree hot/cold 8 gallon per minute monster or an ultra high pressure 175 horsepower 40,000 psi 6 gallon per minute dragon slayer. The slayer can remove pool plaster down to gunite in half day by running an 800 CFM vacuum blower for water extraction and filtering...

HighPressure

incorrect information regarding direct drives over speeding the pumps. The pumps used on direct drives have smaller sized water pumps which can deliver the same GPM as a belt drive and same psi. The pumps don't last as long because they MUST be driven at much higher rpm's...which is the same for any other pump or most machinery in general. However, they are engineers by the pump manufacturer to be run at the higher rpm's. My 7k psi and 40k psi pumps run at much lower rpm's than your belt drives...and thats because they are very large pumps and are meant to last forever...they just get rebuilt as needed. Most of the issues with direct drives has to do with needing a pressurized water supply, the unloading of water directly back into the inlet port, and using "cheap" parts.