Recently, after playing on the new world generation for a while, I realized I haven't heard cave sounds in survival much. I decided to test it by going caving normally (using the worldgen datapack) with the f3 menu open and kept my eye on the Mood% the whole time.

What I expected:

Every once in a while, the mood would hit 100% and play a cave sound

What Actually Happened:

The mood never went over 30%, and spent most of the time hovering under 10%. No cave sounds ever played.

I went caving in the normal way most people do- lighting caves up with torches as I went along, and mining any ores I came into contact with. The whole trip lasted a bit over an hour. When I ran out of food and decided to go back to the surface, my Mood% was at 0. It was a huge cave system, so I spent the whole time exploring and mining ores. No strip or branch mining, and no stopping to smelt ores. 

After some more testing. I found out that this is a problem with bigger caves. Standing in smaller caves, like the old carvers, will still increase the mood even with a couple torches down. However, standing in the middle of a moderately large cave (air space of about 20x20x10 or bigger) causes the mood to decrease steadily with just one torch next to the player.

The algorithm itself might be the same as in 1.16, but since caves have gotten so much bigger it no longer adequately serves its purpose. Practically speaking, players will rarely if ever experience cave ambience in the new caves.