The obvious answer to "why" is that you can use Antarctica as a low(er) cost, low risk, practice run. Similar to space tech of the 60s, the tech developed this way could have a big impact on many areas of life. And yes, it won't solve everything, nor give us a second planet.
Raising radiation levels is not a problem here on earth at all. Not sure about gravity and health effects, maybe it can be simulated with some amphetamine + sedative cocktails.
Hard thing in living on Mars is not the cold, it is the lack of oxygen or easily accessible water. All of these are abundant on Antarctica so it is not really a practice run.
I see little point in exploring this on Antarctica which is why I believe no one really is entertaining idea of this type of test run on Antarctica.
Why should anyone do anything, really?