To make an example and show of force.
Look, the guy, by the law, has been trespassing. It was never his land. Even adverse possession generally requires you to not only occupy the land, but to improve it and pay taxes. This may not be the same everywhere, but it's the general idea. He doesn't occupy the land exclusively (for grazing, maybe, but grazing lands are generally open to other use), and he's certainly not paid the taxes (fees) on that land. The improvements are moot against the other two. That being said, the federal overreach here, spending more than twice what the actual fees (and interest, admin fees, and penalties) are to deal with this is wrong. I'm no fan of the fedgov in this respect, but Mr. Bundy is also not standing on solid ground.
>> “Look, the guy, by the law, has been trespassing. It was never his land” <<
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Your ignorance is impressive.