Preamps are (more often than not) pure analogue devices. Certainly all the shiit ones are.There’s no reason not to include it
Today bass management is typically and more effectively done with DSP digitally, either in the DAC, or in a digital to digital device upstream of the DAC.
It makes more sense to ask "why not put a proper preamp with variable gain, and analogue volume control into a DSP Dac?"