Marriage, kids, other interests - life getting in the way. Transitioning from all-encompassing guitar sonic architect to part-time rock star?
One theory I muse on sometimes on this very question relates to the way The Edge's sound is intertwined so strongly with guitar effects. But particularly that (as he's stated himself) that multi-effects gear might do one thing well, but not others, and throughout his career he's been very good at creating memorable sounds through sometimes innovative use of certain items of effects gear. There was the gritty analogue delay (echo) effects from the Electroharmonix Memory Man pedals in the Boy/October/War era. Then the precise crisp digital delay of the Korg SDD-3000 unit (~Unforgettable Fire era). But while he later used different units for delay (e.g. TC-2290 units were a mainstay of his on-stage rig for decades), he appeared to retain the SDD-3000 for its unique pre-amp which underpinned his signature thick, clean but on the edge of breakup tone. Then with AB the band ushered in an entirely new sound: a vital part of this was The Edge's adoption of the Korg A3 - of the 99 preset sounds on the guitar expansion card for that unit one finds many presets that with only minor tweaks are unmistakably tied to the AB / Zooropa era (Mysterious Ways, UTEOTW, The Fly, Lady With the Spinning Head, Zoo Station, Numb, etc. However, from the 2000s, guitar effects gear has increasingly moved into the digital domain with ever improving amp modelling, generic but highly tweakable effects, and ever more flexibility in how the effects chains are structured. For years now we've seen The Edge's effects rack is dominated by AXE-FX units - I wonder whether this has created a homogeneity that has robbed him of an opportunity to find an innovative connection with a uniquely sounding effect or unit, instead of sitting at his laptop for hours into the night at U2HQ trying to find the supposed perfect sound for a given song. To me this has led to atrocious misfires - personally I find the hollow fuzz guitar chords on The Miracle (Of Joey Ramone) to be a particularly uninspiring recent example. Ultimately, though, in no small part I'd go back to the age factor - an ambitious, young, agitated, energetic artist in their 20s (i.e. 1980s U2) throwing themselves with total commitment to their craft surely has more creative currency than a 50-something millionaire part-time rock band member...