We are told by people that their ailments were cured by God. People claim that God made their cancer go into remission, for example. So why can't God do that for everyone?
Various reasons.
Unbelief is one of these reasons.
Those who have cancer and deny God exists, or believe He exists but hate Him do not generally ask God to cure their cancer.
Some believe in God and have cancer and ask Him to cure it but He does not cure it. God has a specific plan for humanity and this plan entails that some people are not cured from cancer even if they want to be.
God has a specific plan for humanity and this plan entails that for the most part, life is ordered according to certain laws that have been established by God. If a person smokes cigarettes all of their life knowing that they have an increased chance of getting cancer, and then do, then pray to God to cure them and then get mad when He does not, then the person is just being a big baby, crying and whining that they cannot have everything the way they want it.
If a person has sex with whoever will give it to them whenever they can get it, and then get an STD and then pray to God to heal them and He does not, then they again, are just attempting to use God like they have used others to get what they want.
God is not bound to bow down and cater to the sinful desires of fallen man or to be there every time you want something.
So this is one reason why many are not cured of their ailments.
A loving father does not give their child everything the child asks for. The father knows what's best.
As I stated, those that do rely in and trust in God's mercy realize that either way it goes, they will one day die. This is inescapable. So even when God does not answer their prayers in the precise manner they would have desired, they still trust Him to do what is right.
Ok?
We are expecting God to do what people already claim that he does.
And you should expect Him to. He is even now throughout the world.
The testimonies of literally millions exist to bear this out.
As long as you remain in unbelief, you cannot see the Kingdom of Heaven.
Does Heaven have evil on random days? Will people in Heaven die of painful cancers?
I think you know the answer to both of these. The fact that you are asking such questions causes me to question why you are asking them.