"呪" to "恨", but not "怨". Why?

knell

So it looks like Sadako's ultra rare skin's "weapon" changed from the default "呪" "Noroi" (Curse) to "恨み" "Urami" (Grudge or Resentment).

There are usually two ways to write "Urami", both meaning practically the same. 恨み and 怨み. I didn't know the difference, but something felt off about 恨み, so I looked it up. Apparently, 恨み is often used in more normal, day-to-day circumstances, where someone may feel toward another person. 怨み is apparently more deeply rooted, and often used in a more spiritual circumstances. For example, the word "Onryo" is "怨霊" (Vengeful Spirit).

So is there are reason why 恨み was used over 怨み? It may just be me not understanding the nuances, but it would seem like "怨" would have been more appropriate. I'll tag the Japanese community manager, since he could probably explain it to me better. @Donnary21st_BHVR