Not an expert, but I can come up with some plausible sounding reasons.
Ice melting decreases albedo causing increased warming. Keeping it at the pole keeps it from melting.
Melting at the pole will result in ice that is current sitting on land moving to water, significantly increasing ocean level. Replacing a trillion tonnes of ice with a trillion tonnes of water at the pole, even assuming both are at exactly 0C, introduces a lot of energy to the system (333 quintillion joules, aka 333 exajoules. Wolfram alpha helpfully tells me this is about the total amount of solar energy that hits the earth in ~30 minutes, or 0.93x the total human energy consumption in 2010). It stands to reason that introducing that much additional energy to the antarctic system will increase ice melt and the chance/amount of ice sliding off of land into water.
The fine article includes some comments about how this big chunk of ice could get in the way of ecosystems.
Ultimately I doubt we can stop a trillion ton glacier from doing what it wants without expending absurd amounts of energy (to our detriment). But if we could snap our fingers and keep it where it is, I'm pretty sure we should.
