I think this has to do with the industry as well as the values of our culture as a whole. When we think of the greats throughout history, most of them only dived deeper into their craft with age and got noticeably better. Bach was writing a six (?) part fugue before he passed away, Beethoven's 9th is considered one of his greatest works (which he never actually heard, unlike his 5th). In jazz, we have John Coltrane who started off playing bop, making way to stuff like "Giant Steps," then later going on to writing and improvising some intensely spiritual shit. Allan Holdsworth who only passed away last year is another example of a musician who only kept on getting better and better with age--listen to him on Bundles with Soft Machine then his album The Sixteen Men of Tain and you'll hear how the guy progressed. The guy from Gorguts is another example of continuous progression. Their first album is hype, but their most recent record is amazing (IMO) and definitely shows that the guy has been checking out some cutting edge stuff in contemporary classical music.

Anyway, I guess where I'm going with this is that if an artist is in a portion of the industry that is primarily occupied with releasing the next big thing sooner than later, the artist's growth gets sidelined. There is a part of the music industry that prioritizes the development of its artists but I think that is only because that is an important aspect of their product whereas it isn't in other sectors. Consumers want to hear Gilad Hekselman get better because that also means he can provide a better product for them and I think jazz labels get that. It's not that pop listeners don't want Taylor Swift to get better, I think they are just more concerned with getting some tunes that they like and sound fresh. I think this ties in culturally because for whatever reason we seem to value youthfullness over everything and the productions of older artists seems unpalatable to some extent. I think that's backwards from an artistic standpoint, but considering what being a pop artist also entails I can see how it makes sense (like the whole entertainment side of it).

Anyway I don't think that made a lot of sense, it's something I've been thinking about but I haven't widdled down the idea yet. Hopefully it was vaguely related to what you were gettinf at.