PopFly
War Child
I wouldn't doubt Edge has come up with hundreds of ideas since 2020 (minus even the SOS material). Any mere competent songwriter can sit down on a computer and churn out a decent sounding instrumental within minutes or an hour. And if you're in a position to hire an engineer every so often to help flesh out everything, those ideas can turn into listenable instrumentals very quickly. But if Bono can't write a decent lyric or melody for the life of him over one of those tracks, no matter how good it sounds (and is the common thing songwriters face, even the "professional" ones), then those great sounding instrumentals get cast aside. And you start from scratch on new ideas - or attack the older ones that had potential once you've had some time away from it. Hence the "tinkering" or whatever else. You come up with new ideas to top the "mid" ones you came up with over a year or two, or you try your hand on making the arrangement or lyric a bit better than what you had. Intentions or commercial aspects might vary on the person, but working on songs until they're releasable is just part of the process.
Well put. Plus there's the added difficulty that all four guys have to sign off on the idea (no matter who "actually" wrote a given song), plus the fact that so many great U2 songs have come from this very process. As much as we can point to how tinkering or overcooking can lead to some watered-down songs, U2 has had plenty of success in matching random guitar part A with obscure bass track B and half-finished Bono lyric C and suddenly it's a single.