It goes like this:
If there is a God that wants us to know him and wants us to have a relationship with him; why is he hiding from us?

God's propensity for hiding is even mentioned in the Bible in Psalm 22:2, "O my God, I cry by day, but you do not answer, and by night, but I find no rest." (Although I find this more about the futility of prayer) and Isaiah 45:15 "Truly, you are a God who hides himself, O God of Israel, the Savior."

Salvation through belief
If God refrains from showing Himself, logically, He either doesn't want us to know at all that he exists, or He doesn't want us to know yet.
Either way, in hiding, God robs us of salvation.

Ephesians 2:8-9 tells us that salvation is attained by grace, through faith in Jesus Christ and not through our own effort and works.
Salvation is not earned, it is achieved by belief in God.
This puts us in a very precarious position. Without a belief in God salvation is unattainable, yet God (the one who wants to have a relationship with us) refuses to interact with us in any form that would convince us he is actually real.

Whe I was younger there were several ladies I wanted to have a relationship with. Hiding away from them turned out to be the worst way to accomplish this.
I found that going up to them, introducing myself and starting a conversation seemed to be the best and most effective approach.

If a young, ignorant me could figure this out, how is it possible an omniscient God cannot grasp the concept?

A similarly concerning idea - if grace is granted by God, it means He chooses who to grant it to. It is not the fault of those to whom it is not granted if they face eternal damnation.
Remember, it is not by works (the deeds you perform on Earth) that salvation is achieved but by grace.

Common apologetics for God not showing up

1. You cannot survive seeing God in all His glory
   How often haven't we heard the apologetic from Exodus 33:20 that says anyone who sees God's face will die?
   Well that simply isn't true.

   Many people not only saw God, but had conversations with him; these include Moses (Exodus 3:2), Abimelech (Genesis 20:3), Solomon (1 Kings 3:5), among many others.
   God interacted extensively with Adam in Genesis 2:16-18 when He told Adam not to eat from the forbidden tree and in Genesis 2:19 where God brought him all the animals to name.
   In Genesis 3:9-13 when they hid after eating the fruit.
   God spoke to Eve in Genesis 3:16 then Adam again in Genesis 3:17-19.

   Clearly, seeing God's face is no problem, so there should be no problem for him to continue showing it.

   "Yes, but" I hear the apologists clammering, "in all those instances God hid His face".
   Really? Every time?

   What about when Jacob wrestled with God in Genesis 32:22-32, did He hide His face during that entire bout too?
   Even when He had to cheat to win (Genesis 32:25)?

2. Free Will
   Seeing God would impinge on your free will; you would no longer have the need for faith.
   There are two concepts to deal with here:
   1. Impinging Free Will
      The concern is, if God were to remove all doubt he exists by showing up, our ability to act in any way other than He dictates would be curbed.
      We would be absolutely unable to 'sin', removing our ability for 'soul growth'.

   2. Losing Faith
      In this instance faith is used in lieu of 'just believing for no good reason'.
      Believers pin a lot of emphasis on needing to 'be faithful', 'having faith' and 'being strong in your faith'.
      Is it true? Would believers lose faith if God appeared?
      Well, they would change from believers to knowers, from agnostic theists to gnostic theists.
      Isn't it better to know something than to believe it?
      If the answer is 'yes', then there is no place for faith if God were to show Himself and the point would become mute.

3. You couldn't reject him
   This supposedly is a consequence of the free will mentioned above.
   If God were to show Himself, people's free will to reject Him would be eliminated.
   This is simply not true. If God were to show Himself, I would have to acknowledge He exists, but I would still be able to reject Him in every other way.

   Hitler (yes, I went there), for example, was undoubtedly a real person, and we would be perfectly within the bounds of reason and morality to reject his actions, his policies and his worldview.
   His being real wouldn't affect the way we accept or eject him any more or less than if he were a mythological character.

If God is capable of revealing himself to us and is able to manifest in reality and doesn't do so that leads to a logical contradiction
- i.e. God wants us to know he exists but does not reveal himself to us although he is perfectly capable of doing so.
This logical contradiction shows that God cannot exist.

The Schellenberg Hiddenness Argument describes this in a deductive argument

1. If no perfectly loving God exists, then God does not exist.
2. If a perfectly loving God exists, then there is a God who is always open to personal relationship with each human person.
3. If there is a God who is always open to personal relationship with each human person, then no human person is ever non-resistantly unaware that God exists.
4. If a perfectly loving God exists, then no human person is ever non-resistantly unaware that God exists (from 2 and 3).
5. Some human persons are non-resistantly unaware that God exists.
6. No perfectly loving God exists (from 4 and 5).
7. Therefore: God does not exist (from 1 and 6).