I suspect you've been looking at poor reproductions online. Adams spent quite a bit of time railing against the "chalk and soot" nature of photographs that don't maintain detail, or, at a minimum, texture, in both the highlights and the shadows. If you read his descriptions of how he made many of his photographs, you'll see that he would take pains to put the darkest parts of the image on zone 3 (perhaps zone 2 if he was feeling bold), and then develop for the highlights. It became such a scientific approach for him that one could argue his artistic vision ceased and he became almost purely formulaic. Perhaps you can identify some of the "many" Adams photographs with complete blackness?
As selling Adams' photos became good business, newer compilations of his work started to pile up. And that sadly meant quality "had" to go down.
On line is not the only source of bad reproductions. And the "400 Photographs" is the biggest, shameless publication of them all. It has a LOT of photos with black holes (and forget brilliance or tonality) that even in his calendars were much better reproduced, plus there should have ever been 400 photographs in one book to start with, as it sadly showed Adams' sameness, lack of photographic vision and as result, supporting all negative opinions of his work. The book of course has not put a dent in the sale prices of his originals, but successfully diminishes his purported life time achievements on aesthetic levels. Or perhaps arsthetics as
@Alan Edward Klein likes to put it
As for detail in shadows, we could argue for the rest of this planets life whether viewers are first drawn more to highlights or shadows. An articulate composition will take care of that.
If we make photographs for viewers to approve, we are not presenting our own vision of a scene. So kick ass, stand up to the norms, make those shadow details visible to the last hair or black them out, it's your choice. Now, when lack of shadow detail becomes a felony, you may have to reconsider.