As the son and grandson of amputees I have wondered the same thing. Or why doesn't He raise another body like that of Lazarus that has been dead for three days?
The answer is that Jesus and the Apostles performed gifts that were Signs,indisputable evidense to anyone other than a fool. Healing today is an answer to prayer but it is not intended purely as a miraculous sign.
God chooses to perform miracles that give skeptics a little room to doubt. Even the story of my healing can be dismissed by a skeptic as a spontaneous remission,which are documented to occur now and then. I am impressed that my spontaneous remission came immediately after intercessory prayer as outlined in scripture in the New Testament book of James. Another man,being a skeptic still has enough room to attribute my miracle to something other than answered prayer. If God healed an amputee or raised the long dead,it would constitute a Sign and for the time being God has chosen not to act in that manner.
What is interesting is that even when He has performed miracles that are clearly signs,people have still refused to believe despite what they have seen with their own eyes.
God will not suspend your free will to believe or not,that is the summation of what I have written which I believe accurately reflects scripture and experience.
