Custom cabinet work does not have a low bar. You need to be familiar with multiple joinery techniques and finishing methods, even if your parts are coming straight off a CNC. Getting them perfectly square, face framed, mounted etc takes a lot of time and attention. For houses where the framing was done poorly, it takes even more time.

I believe fairly competent cabinet assemblers / installers are making $40-75 / hour depending on location. Everyone else paying less is half-assing it or doing a poor job.