Jesus was merciful and he could cure any disease, he discarded his jiva and was one with universal consciousness. He saw unity wherever he went and with true unity comes unlimited power, which we know as miracles. Jesus could have instantly cured everyone on the planet but this would have been a violation of free will. Let each soul walk its path. No one is born by accident and those who enter the world with disabilities have done so of their own choice. People die, largely speaking, because they have completed what they took on physical form to experience, it has served its purpose and so they dissolve themselves. Birth is the onset of the idea that you're separate, death is the dissolution of it. And of course, there are many other religious philosophies concerning why people die, with one of the most well-known being karma.
Karma is wound up in the jiva (personal identity) and it brings to mind something Mahavatar Babaji said to Lahiri Mahasaya when he was describing the latter's death in a previous life: "You slipped away and vanished into the tumultuous waves of the life beyond death. The magic wand of your karma touched you, and you were gone! Though you lost sight of me, never did I lose sight of you! I pursued you over the luminescent astral sea where the glorious angels sail. Through gloom, storm, upheaval, and light I followed you, like a mother bird guarding her young. As you lived out your human term of womb-life, and emerged a babe, my eye was ever on you. When you covered your tiny form in the lotus posture under the Nadia sands in your childhood, I was invisibly present! Patiently, month after month, year after year, I have watched over you, waiting for this perfect day. Now you are with me! Lo, here is your cave, loved of yore! I have kept it ever clean and ready for you. Here is your hallowed blanket, where you daily sat to fill your expanding heart with God! Behold there your bowl, from which you often drank the nectar prepared by me! See how I have kept the brass cup brightly polished, that you might drink again therefrom! My own, do you now understand?'