People do not have enough faith whether they believe God cannot heal,or does not want to heal them.
Some people depend more on God when they are not healed and they are in a better place spiritually which is a better benefit.
Some people if healed may start sinning because of their healing as someone in a wheelchair with muscular dystrophy that might be out going to the bar,and chasing after women,and drinking,which he is in a better position by being in a wheelchair.
Jesus said if your hand offends you cut it off,or if your eye offends you pluck it out,for it is better to enter life maimed than to have 2 hands or 2 eyes and lose out because of sin,but of course He does not want us to do away with a body part,but illustrating the point to abstain from sin.
So people not healed might cause them to be in a better relationship with God,and may cause them not to sin,and God knows the condition of the person whether a healing is good or not good for them and He will look at it from a spiritual perspective in their life for the good.
2Co 12:7 And lest I should be exalted above measure through the abundance of the revelations, there was given to me a thorn in the flesh, the messenger of Satan to buffet me, lest I should be exalted above measure.
2Co 12:8 For this thing I besought the Lord thrice, that it might depart from me.
2Co 12:9 And he said unto me, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me.
2Co 12:10 Therefore I take pleasure in infirmities, in reproaches, in necessities, in persecutions, in distresses for Christ's sake: for when I am weak, then am I strong.
Paul received a thorn in the flesh,an infirmity,so that he would not exalt himself to think he was something great for then God could not work in his life,for God resists the proud but gives grace unto the humble.
So people may say God will heal everyone,but Paul was given an infirmity to keep him humble for then he was in a better spiritual position with God,and depended on Him,for when he is weak then he is strong for the power of Christ rests upon him.
So is it better to not be healed for then we will depend on God more,and the Bible says the Son learned obedience by the things that He suffered.
But God knows our situation and what will cause us to be in a better spiritual position with Him for that is what truly matters.
To heal or not to heal that is the question,and the answer is in yourself how it will affect your relationship with God.
2Co 6:4 But in all things approving ourselves as the ministers of God, in much patience, in afflictions, in necessities, in distresses,
2Co 6:5 In stripes, in imprisonments, in tumults, in labours, in watchings, in fastings;
2Co 6:6 By pureness, by knowledge, by longsuffering, by kindness, by the Holy Ghost, by love unfeigned,
2Co 6:7 By the word of truth, by the power of God, by the armour of righteousness on the right hand and on the left,
2Co 6:8 By honour and dishonour, by evil report and good report: as deceivers, and yet true;
2Co 6:9 As unknown, and yet well known; as dying, and, behold, we live; as chastened, and not killed;
2Co 6:10 As sorrowful, yet alway rejoicing; as poor, yet making many rich; as having nothing, and yet possessing all things.
Rom 8:35 Who shall separate us from the love of Christ? shall tribulation, or distress, or persecution, or famine, or nakedness, or peril, or sword?
Rom 8:36 As it is written, For thy sake we are killed all the day long; we are accounted as sheep for the slaughter.
Rom 8:37 Nay, in all these things we are more than conquerors through him that loved us.
We know we will go through trouble from the world as they persecute,and other troubles,so it would appear if God healed everyone no one would ever go through trouble in the flesh,and never be persecuted.