So I guess I would say there are three factors I was considering when I wrote this.
1.) Good for Sales: Is it more beneficial for WotC to resell updated "Core" material (a new PHB, a new Planar book, a new Eberron campaign guide) than it is to sell augment material (a supplemental book of PC options, a deep dive into a specific plane, an adventure set in Xen'drik)
2.) Good for Bloat: Does resetting the game effectively kill bloat by replacing "outdated" versions of stuff with newer versions? Is it in players and DMs interest to no longer have to worry about balancing and updating things like psionics, incarnum, or other rules like that when upgrading to the next version? In essence, to wipe the board clean from all the supplemental chaff and start fresh?
3. Good for the Game: Does making monumental changes that invalidate the game ultimately make the game better or worse? There is no reason for a 5e player to seek out Complete Arcane; there is at best limited value in acquiring a copy of Tales from the Lance Boxset or The Village of Hommlet module. On the one hand, it keeps 5e players focused on what is available now rather than seeking out OOP books. On the other, it makes collected volumes of older material of limited or no value (barring a tremendous amount of work for conversion or just as inspiration).
To ansswer my own questions: I think one is important to WotC as there is a law of diminishing returns on the sale of esoteric items. I think two serves a useful function of pruning deadweight, but I also think three should be more important than it's been treated, despite the fact it clashes against 1 and 2. Because I would have loved to buy additional Eberron material that expanded the world over the past few years rather than rebuy the Eberron Core setting book (because I need the edition specific versions of the rules) over and over again.