What is the mitigating factor with cleanup? Do we lack materials that can survive the extreme levels of heat and radiation? Are we unwilling to pay the cost?

What is the mitigating factor with cleanup? Do we lack materials that can survive the extreme levels of heat and radiation? Are we unwilling to pay the cost? Or, is the problem a lack of sufficiently complex robotics that can perform the necessary tasks at a distance? If the problem is materials, we're in trouble.