The problem with revoking the estates is that there is nothing to prevent them from snatching the estate right back up (unless the lord uses his or her hours to start destroying/re-partitioning estates, which may screw with their tax income in a negative way). They could even wait until right before turn change and retake the estate (or another) to make sure they get the gold.
Not to mention that you KNOW they will leave the realm if they're banned. If their estate is simply revoked, it may annoy them so that they DO start spying on the realm out of anger.
