A statement from DEFRA: "We don't comment on leaked documents or provide an ongoing commentary on discussions with other departments. The package for English farmers has been met out of Defra's existing budget. However we do not yet know what the full cost of this outbreak will be or whether this can be met in full by the Defra budget. Scotland and Wales are considering their own measures to assist farmers."
So we may never know why or if the Treasury pulled the plug on the package.