The question of why Jesus heals people with certain ailments but not others is an interesting one. My guess is that it may have something to do with him being a fictional being, but I will set that aside for now and consider three other overlapping possibilities. The astute reader will likely protest that these are not three different possibilities at all but merely minor variations on the same. I won't argue with that.
Part of God's Plan
First up, we have to consider the possibility that the ailments Jesus won't heal serve a purpose in the grand plans of some sort of god. Just because we are not informed about the nature of this plan does not mean there isn't one for each of us. If the contents of the "holy" bible provide any clue, this is a god that really enjoys testing people with suffering. Perhaps the ailments that are never healed fit into that cruelty somehow. After all, it is rather difficult to read that particular book and not come away from it convinced that this god is monstrous.
I suppose we could conclude, like many Christians do, that testing someone isn't intended to be cruel. Perhaps those who successfully pass these tests will be rewarded. The rest of us might not see the rewards because they might not come until the person has died. That seems more than a little far-fetched, but this is how some Christians have tried to explain this.
They Deserve It
Next, we can consider the possibility that various ailments are not only part of the plans of some sort of god but that this god caused these ailments to punish deserving "sinners." More than a few Christians have suggested this possibility. If someone has an ailment, they reason, and their prayers for assistance go unanswered, perhaps that is because the ailment is a form of divine punishment. In short, they are getting what they deserve for violating some sort of godly command.
With this line of thinking, it makes perfect sense that these people wouldn't be healed because they don't deserve to be. They are being punished, and whatever ailment they have is one they've brought on themselves. So much for empathy I guess.
Mysterious Ways
Ah yes, the most popular non-answer answer! We'll just assume that Jesus isn't healing various ailments because...reasons...and move on. Nothing to see here. We don't understand because we aren't meant to understand. This has almost become Christianspeak for "I don't know" except that it seems far more dishonest than "I don't know." And unlike "I don't know," I suspect it is designed to end the conversation as quickly as possible. This is the Christian's way of saying, "I don't want to talk about this anymore" without having to do so.
One of These is Worse Than the Others
Even though these three possibilities overlap considerably, the second one (i.e., they deserve it) strikes me as far more problematic than the others simply because it affects how the afflicted is treated by others. Some Christians see little reason to be kind to someone whose suffering they attribute to divine punishment. If they believe that this person is getting what they deserve, their compassion evaporates quickly. Who are they to question what their god is doing? And so the person who is already suffering with some sort of ailment now has to contend with unsympathetic Christians on top of everything else.
