Think it's partly having too much caffeine, and getting bored with lighter roasts. The expensive, more recently roasted, single origin coffee has retained a lot more of its nutrients - including caffeine.
I think the craving for occasional metallic mud has to do with craving a darker roast, more char, more age and antioxidants, and a break from the insanity of fresh caffeine.
I used to make wine, and at first I loved the freshness of a new batch - sometimes I wouldn't age it at all after fermentation, and it would only be like 9% ABV, almost tasted like grape juice still. Was enjoying that for a while.
Then one time I had an old dusty corner store bottle that had been sitting on a shelf in 90F. It was like 7-8 years old and basically ruined. But it was amazing... it was like black in color, tasted like rotten raisins and a hint of vinegar. But I hadn't tasted that age in a long time.
So then for a while I started to enjoy cheap, old, ruined wine from the corner store in the same way you might enjoy that ass dirt shit coffee.
My present weird obsession is cheap black tea, unsweetened. I drink it by the cup and make cold brew in the fridge for 15 hours at a time. Amazing.