Think thereās a bunch of reasons. But for sure, Endtroducing is bordering on a āplunderphonicsā type record, which means it was technically difficult to make at the time, and pretty much a dead artform due to copyright issues since the 2000s. Hasnāt lent itself to huge waves of output as a result.
I think instrumental hip hop is a bit of an oxymoron anyway. The music was invented to be rapped over and requires space for that, most of the genres best producers arenāt in it for making instrumental music (though you do get stuff like the Petestrumentals LPs by Pete Rock). A lot of the best instrumental hip hop albums are probably the instrumental versions of rap albums that Iād almost never recommend over the real thing (the instrumentals to, say, Aquemini or The Cold Vein are incredible but offer little over the actual albums). Most of the stuff on Endtroducing wouldnāt make for great rap music, and DJ Shadow has always struggled making great music for people to actually rap over IMO.
There are plenty of great examples of instrumental hip hop albums form the likes of J Dilla, Madlib, Nujabes etc., and some producersā beats sound great when isolated on instrumental LPs ā like Clams Casino or El-P. There are also countless examples of electronic music that fuses in hip hop and breakbeats. But as soon as you start to diverge too much from rap, it starts to sound like or be labelled as something else (Endtroducing often has as much in common with coffee table Trip Hop type stuff to me).