See, Clarke, now you're doing a 'James'. Lazily throwing out a trite question, making no qualified statement of your own. Tell us what your expectation of proof of God would be. A king type person sitting on throne of gold in a big castle? What?
Firstly; your question assumes that God is an object among other objects, in other words - something you could locate under a microscope if He were “real enough.” But if God exists as the ground of being itself , the source of existence rather than one existent within it; then He doesn’t “hide,” because He’s not that kind of thing. Asking why God hides is like asking why logic can’t be seen through a telescope.
Secondly; God doesn’t hide; he’s written into everything. The order of the cosmos, the fine-tuned precision of its laws, and the mathematical coherence behind reality all scream of design, not accident. So, much so, that idiots have to invent fairy tales about aliens 'seeding' the universe to try and explain it.
God went further: He entered history, in flesh and blood, performed public miracles, was crucified under Rome, and rose from the dead before witnesses who died proclaiming it. That’s not hidden; that’s recorded history.
And now even modern medicine echoes the same truth: thousands clinically dead have reported a consciousness more vivid than life itself. The evidence of God is overwhelming.