This is a question that has been asked by a disgruntled atheist. Atheists always question our faith, but they never question their own faith in logic, reason, and science, though these all come short and are limited in what they can do.
Deuteronomy 29:29 The secret things belong unto the LORD our God: but those things which are revealed belong unto us and to our children for ever, that we may do all the words of this law.
We do not worry about the things that God does not do; we know nothing about that. We are concerned about what God does, and we know that God heals. No one disproved that the man in John chapter five was healed of his impotency. I am sure that every Pharisee and scribe would have done so if they could. No one disproved that the blind did actually receive sight. No one disproved that Lazarus was raised from the dead. I am sure many would have done so if they could.
We also know that God saves sinners (1 Tim. 1:15), that God created the earth, that Noah built an ark and weathered a universal flood, that Jonah was swallowed by a great fish, and that Lazarus was raised from the dead. We know this by faith the same way that you know certain things by your own faith: evolution, uniformitarianism, transcendental knowledge, aliens, and ghosts, which are all purported by scientists.
If God decides to heal a liver rather than an amputated leg, that is his business, not ours. The secret things belong to him.
Why is it so that you do not distrust science, since there are many things that science cannot do and has not done. Why cannot science heal an amputation? Since your faith is in science, that would be your question, and it is mine, also. Can you give a reasonable answer to that? Why cannot science raise the dead?
God can do anything he purposes, but he does not do them at our whim but according to his own will and purpose: Daniel 4:35 And all the inhabitants of the earth are reputed as nothing: and he doeth according to his will in the army of heaven, and among the inhabitants of the earth: and none can stay his hand, or say unto him, What doest thou?
Let God be true and every man a liar (Romans 3:4).