The idea that you cannot attain perfect pitch as an adult has been thoroughly debunked. The University of Chicago’s study is most famous but results have been replicated at many other schools. Adults can develop perfect pitch just fine.
The issue seems to be that most adults find it useless and as artists they’re better off spending their time elsewhere.
This isn't quite right; the University of Chicago study replicates what has already been known for a long time - that musicians can develop their pitch memory around the timbral context clues of a particular instrument. However, this learned pitch does not generalize to other instruments and/or common everyday sounds (train horns, washing machine vibrations) in the way that people with absolute pitch can instantly identify.
An analogy to this might be that a colorblind person if shown enough fabric and told what the colors were can eventually associate the texture of the fabric with a given color and can learn to do this translating in their head, but they will not be able to train their eyes to see color no matter how much practice takes place.
If it were the case that such a substantial number of amateur test subjects could develop absolute pitch from doing a few exercises, we would expect to see commensurate numbers of musicians who spend thousands of hours playing music to also develop this skill, but this is not and has never been the case.
Yes, the biggest problem to acquire perfect pitch is that Western music is made exactly to wash away the difference between keys. Instruments are designed so every key is relatively the same. Things would be different if every key had a slightly different relationship. This used to be the case in medieval music, that's why early composers thought about different keys having different moods.
That statement is not true of Western music in general, only of most (not all) classical and poular music since roughly the 18th century, when "equal temperament," tunings designed to make all keys sound the same, became popular.[1]
Much Western music, such as that written during the the Baroque, Renaissance, and medieval eras, as well as certain modern genres like barbershop quartets, modern classical, electronica, microtonal and atonal music, etc. use a variety of other systems such as some form of just intonation[2], where different keys sound very different as they exhibit differently sized versions of the same interval.
Conversely, much non-Western music also uses some kind of equal temperament (where keys all sound the same), such as Chinese, Arabic, Indonesian, Thai, and Native American music.[1]
I hadn't actually heard of the Chicago work before, but this is interesting:
"These results suggest that the acquisition of intermediate absolute pitch ability (significantly above chance but below ‘‘true’’ AP performance) depends on an individual’s general auditory working memory ability" [1]
Apparently learned absolute pitch wasn't as accurate as "true" perfect pitch.
The issue seems to be that most adults find it useless and as artists they’re better off spending their time elsewhere.