Most harnesses don't have solderless connections.Some folks don't live close to a good tech. Some folks may have impediments that would make soldering difficult or impossible. Some folks are happy to support others that are trying to make a living.
If I buy a soldered wiring harness, I buy a one with solderless pickup connections so I can stick the pickup wires into the screw terminals, and part of that's because I like to try out different pickups in my builds. I've never had an issues with any solderless connections.
Anyway harnesses are usually a ripoff because they include and advertise a special tone capacitor, as if it did anything to the tone. No doubt they include quality parts but anybody selling you an expensive tone cap is a paper-in-snake-oil salesperson.

