First, there is a shortage of spirit beasts. There might be a lot of flesh after the spirit beast tide. For now, there are few. The cunning spirit beasts can't be caught without using conventional methods.
When caught, the players chose to use it sparingly among their troops. If the citizens need to eat spirit beast meat, they have to go out and hunt it.
In most cases, the Lords seized these slain or captured spirit beasts for a few rewards. Some heartless lords banned their citizens from having possession of these commodities.
It is, by the way. How these lords govern their subjects is not what we will delve into.