It's for much the same reason you'd struggle to stop an avalanche or a hurricane.

All of the remedies they've tried are ones already tested and modelled like you mention - but at the end of the day this happens so infrequently and under such varying circumstances it's hard to cover every eventuality.

One of my friends pointed out that it's much akin to running one of the mars landers - it takes a long time to sort out what to do, send down the ROV's and give it a shot.