All DACs need a low pass filter to not generate all manner of inharmonic distortion. But a single bit DSD based DAC doesn’t need anything else.
For a 20 bit DAC a thermometer resistor DAC would use about a million very precise (1 part in a million) identical resistors. Not practical 
An R-2R resistor DAC uses two resistors per bit, but the also needs to be accurate to within one in a million for a 20 bit DAC. There are a lot of tricks to do a better job, but fundamentally accuracy is hard.
You can build a great DAC in a lot of ways. But a great ladder DAC isn’t simple and quality costs just like other kinds of DACs.