I'm telling you, there is an inborn neurological and neurodevelopmental thing that is difficult to overcome after adulthood. I can practice a song 30x, move onto another song and practice it 30x, revisit the previous song and need to check the chord sheet because I can't remember all the chords. And we're talking only a five or six chord song here! It sucks.
I hear music in my head all the time, bordering on musical hallucinations. I can tell you what is out of pitch or whether someone is playing in the "wrong" (psycho-acoustically undesirable) key. I can tune using only one reference tone. I can get pretty damn close using no reference tone. I get music composition, timing, and all that. I just can't develop proficiency in playing an instrument. I mean, maybe I could if I became obsessive about it and be one of those people who spend four hours per day but I don't think anyone "chooses" to become obsessive about anything. Actually, I couldn't play four hours anyway because I get muscle cramps and fatigue after about 40 minutes. My fingers just cease to work with finer dexterity and become more like paws.
I recall it being much easier when I was 16. I shouldn't have taken that 20+ year hiatus!