Black color coming from projector isn't full black either https://www.projectorreviews.com/articles-guides/projector-b...
Have you seen those samsung qdoleds? In a normally lit room they look more washed out than a VA panel, yet somehow still having an "inf" contrast...
On the other hand, there's very little light spill from DLP--- and what little there is, is attenuated by a really big factor by the LCD.
I'd guess the limiting factor is light scattered elsewhere in the room and by the front surface of the display.