I don't know why manhwa in particular do this non-chronological storytelling often but I think it's because they're serial releases. They have to hook the audience with little hints of what's to come so the views increase exponentially each week. It seems useless and unnecessary to us who are already interested but think of the team developing this who will lose resources (or risk future seasons) if they don't gain enough views. In a world where there's literally hundreds of webtoons you could be reading, they have to give you reason to read theirs. Like why did the MC and ML relationship sour if they were such good friends? What happened with the su*c*de attempt? Etc.
I actually thought it was beautifully done and even if it took me a second, everything made sense. The art is so well-conceived, I kind of resent anyone complaining about the pacing. It felt very 'cinematic montage'