Okay, lets try it this way. He started out walking with Adam and Eve. That got forgotten (except for what is written). He spoke to Moses, led His people from Egypt (many miracles there), all of which faded into the realm of disbelief - even among the people from that generation. Daniel in the fire - never mind that, it never really happened... etc, etc.
But He HAS revealed Himself to us through His Son, this last time. We only have to look to the Son to see Him, but here we are, so many people disbelieving that this Son ever existed, never mind that He performed those miracles or rose from the dead.
We aren't very good at hearing or seeing
Let's try that Thomas Paine's way - he says it more eloquently than I could.
As it is necessary to affix right ideas to words, I will, before I proceed further into the subject, offer some observations on the word 'revelation.' Revelation when applied to religion, means something communicated immediately from God to man.
No one will deny or dispute the power of the Almighty to make such a communication if he pleases. But admitting, for the sake of a case, that something has been revealed to a certain person, and not revealed to any other person, it is revelation to that person only. When he tells it to a second person, a second to a third, a third to a fourth, and so on, it ceases to be a revelation to all those persons. It is revelation to the first person only, and hearsay to every other, and, consequently, they are not obliged to believe it.
It is a contradiction in terms and ideas to call anything a revelation that comes to us at second hand, either verbally or in writing. Revelation is necessarily limited to the first communication. After this, it is only an account of something which that person says was a revelation made to him; and though he may find himself obliged to believe it, it cannot be incumbent on me to believe it in the same manner, for it was not a revelation made to me, and I have only his word for it that it was made to him.
...
When also I am told that a woman, called the Virgin Mary, said, or gave out, that she was with child without any cohabitation with a man, and that her betrothed husband, Joseph, said that an angel told him so, I have a right to believe them or not: such a circumstance required a much stronger evidence than their bare word for it: but we have not even this; for neither Joseph nor Mary wrote any such matter themselves. It is only reported by others that they said so. It is hearsay upon hearsay, and I do not chose to rest my belief upon such evidence.
None of us are bound to believe ANY of those stories. If they ACTUALLY happened, they ought to be able to happen again in a way that is completely indisputable for any of us, and neither you nor I should share any part of the blame for God's failure in that regard. This God who cannot manage to irrefutably manifest himself to ALL people (as the Sun does) is a piss-poor God - and we can conclude that he is either not real or he is not worthy.