i do have an idea, gave this some thought a few months back

first and foremost, some base points:

1. simon petren and peder elias composed mars and simple joys => as per simon petren's public fb page, they both worked together at the sm studio in nov 2022
2. credited a&r for blossom is kim kyungjoo => they actually worked with sm groups and particularly exo and exo related projects (subunits, solos) up until, from what i can see, 2019-ish. might be wrong about the precise date, one thing is for sure though: i can't find credits of theirs within sm in the last years, the last credit of theirs that i found is for loossemble. anyone do correct me if i'm wrong but either way my point is that they don't work with sm anymore (or if they do, it's not exclusive).
3. we know that for blossom kyungsoo called upon staff that he worked with before => eg lee raekyung/itchcock for the music videos (should have done the same for mok jungwook butttt i digress!)

seems pretty obvious to me going off of that that

1. kyungsoo/css went for demos that had already been presented to him for empathy and/or expectation for the most part
2. their contacts led them to that person for a&r you decide whether 2 induced 1 or 1 induced 2 or 1 and 2 are just concomittant. either way what that means to me is blossom was kind of a transition album, building off what and whom kyungsoo/css knew.

as you said, in the meantime, css hired for a&r, which means they didn't go for the person who worked on blossom. it's too early to tell whether that's them completely detaching themselves from their footing music wise that comes from kyungsoo's background. it does kinda hint that way though, doesn't it?

does it necessary mean we won't see the old producers again? not necessarily, i'd say it's mostly uncorrelated actually - esp considering the fact that multiple producers from the blossom roster are semi-regulars to regular within kpop these days. i do certainly hope though, and genuinely think that means they're expanding horizons. that's also why i say i wouldn't mind kyungsoo taking his time to release dks4 -although from what he's hinted at he seems very excited about it and it's already underway which hey i won't complain lol that's why i'm also particularly happy about ksoo collabing with people now, that necessarily furthers his contact list, timing's good!