Array.Initialize calls value type default constructor via reflection. There is nothing preventing the value type default constructor from getting trimmed. See discussion in #77336 (comment)

However, adding RequiresUnreferencedCode on Array.Initialize has a ripple effect. It introduces warnings in situations where array type is passed into DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All). We have some instances of this problem in our own libraries.