Here is food for thought. Amputees are not healed because no one in these times believes it can be done. There are stories in the Catholic church of amputees being healed but even I see it as a possible legend. So for example since Jesus could not heal many in his hometown because they didn't believe he could do it, so he couldn't. That is in the bible. Plus he often said to people, "your faith has healed you".
Thus I repeat since we humans have a hard time believing God can cause an arm or leg to reappear on someone who has lost their arm or leg Jesus, who is also God, cannot heal us. It is a requirement that someone has the faith that God can and will do it and those people are almost non-existent. I have added another requirement unintentionally but it is also food for thought. What if we believe He can but do not believe he will. The book of James speaks of this saying if we are double minded we will get no healing. So some people know God can replace an extremity but have a hard time believing he will.
So my answer is: lack of Faith and lack of Trust.
peace and good health to you,
God requires people to believe amputees can be healed before he gets off his arse and actually does some healing? What an absolute prick. Can you imagine if the NHS worked like that - "Sorry, nope. The surgeon will not be removing your brain tumour until you believe he can do it." - They'd be struck off! Why do people let god off the hook for such shockingly abysmal and inhumane health care?