It's like, "how can someone so bountiful with brilliant and so consistently ahead of the game, abruptly become barren and boring and out of synch"?
Usually, when it goes, it goes forever. Rarely, though, the magic touch mysteriously regenerates itself - the comeback that is aesthetic rather than simply financial or crowd-pandering.
David Bowie is a supreme example of "on it" / "off it" / "on again".
His "on it" phase runs from "Space Oddity" to "Let's Dance" the single, although there are dips intermittently within that sustained run of brilliance ("Holy Holy" being the most nadir-y, although there's other lapses).
DB's "off it" stretch - if you're being realistic and honest - goes from Let's Dance the album all the way through to 2013. If you want to be charitable or sentimental, you might spare "Little Wonder" or "Loving the Alien" from the stern verdict, or give points for bravery and effort-to-be-interesting with something like Outside. But really it's a virtually unbroken wall of "off it" - and often direly so.
And then (partially) with The Next Day and (absolutely) with Blackstar, the magic's back - mortality quickening the artistic pulse no doubt.
These thoughts were triggered by coming across this impertinent track, created and released in 1997 for a Resonance FM compilation, smack dab in the middle of the "off it" phase, and seemingly prompted by David's dalliance with drum & bass and electronica on Earthling, along with his haircut of that time. There seems to have been some kind of prank involved - an advert in the music papers purporting to be from David Bowie and soliciting for ideas from the general public.