Board Thread:Anime/@comment-39492511-20200807001735/@comment-1327106-20200807013428

The composers are Koei Temco employees. They also compose for Koei's other games like Dynasty Warriors, so they're part of the dev team. They probably did the music because Koei's paying their salaries anyway, and it's their job to score Koei games. On the other hand, Koei would have to pay Sawano extra money to license his music on top of trying to find other things for their composers to do with their time.

This is normal behavior for a Koei licensed title. When they did the Persona 5 Scramble spin-off of Persona 5 (which also has a fan favorite composer in Shoji Meguro), they replaced him with their own composers.