I feel certain they have messed with the battle engine at various points since gen 3 (the way messages and I think animations display for double battles in particular I think has been altered, hell the way things like raids work...) they just like how it works for this. "Why would someone not want to see the exact stat raised each time? It's very convenient!" + "There's not many moves that raise multiple stages at once, so there's no reason to bother" is the exact kind of developer thought I can see that somehow leads to Anger Shell proccing 5 separate times to tell you what changed (They did, incidentally, update this so that Anger Shell only activates once, then it plays the 5 messages, instead of Anger Shell indication then one message, then another and so on)
Legends Arceus did have its own battle engine tweak but aside from it porbably stil lbeing based on the same engine to begin with, I think it just simplified stat messages because stat buffs in general worked differently. There was no raising distinct stats by different stages, so there was no need for it. So they changed it.
See also: Stuff like how there's no mass release option outside of LA, Home & Let's Go because those are "capture" focused games. "Why would you want to mass release in a normal game??"
Just feels like that kind of dev-thought
Legends Arceus did have its own battle engine tweak but aside from it porbably stil lbeing based on the same engine to begin with, I think it just simplified stat messages because stat buffs in general worked differently. There was no raising distinct stats by different stages, so there was no need for it. So they changed it.
See also: Stuff like how there's no mass release option outside of LA, Home & Let's Go because those are "capture" focused games. "Why would you want to mass release in a normal game??"
Just feels like that kind of dev-thought