The small amount of gain required in preamps don’t require class d technology. Opamps the size of a couple grains of rice can already achieve enough gain for preamp use.
Class D is a trade off to gain efficiency, which isn’t needed in lower power situations. Only a moron would buy a Class D hifi preamp.
The first watt is what counts most and that is where Class D cant compete with solid state Class A.
Adding lots of feedback, crossover distortion, switching noise, output filtering, transistor distortion (even trace amounts) destroys the first watt.

