Warranty is the biggest reason for a prebuilt. Anything goes wrong with it and you're not spending money on things to test and experiment with. You send it in, it comes back working.
Lift a car with a hammer. Sometimes the only tool you have access to is the wrong tool. That doesn't make it the best or correct or even reasonable tool to use.
That doesn't apply the same for tools as it does cameras. For cameras the idea is at least you have the image captured. For a tool, if you're trying to lift a car up, a hammer alone isn't going to do you much good.
Dementia may be caused by a prion