I think the reason the Maker is still absent is because the humans aren't looking in the right places. Even the deities or spirits we've seen physically represented in game have only been material reflections of their Fade forms, which are pure magic shaped by belief.
I'll talk about the elven pantheon because it's the easiest. We've seen Mythal and Fen'Harel, Xebenkeck, Gaxkang, and Imshael. But, they haven't always existed in their current forms. Mythal can appear as the human woman who offered her shelter, or a dragon, or a bird, and Fen'Harel is pictured as a canine. Xebenkeck appeared as a desire demon, and Gaxkang initially as an arcane horror. Imshael looked like the guy who sat behind me in history class, wearing Anders' robe.
So how would people recognize the Maker if He walked up and said hi? Are there any actual likenesses of the Maker? What if he shaved his beard?
Take a theory that's been around for a while: Sandal may be the Maker.
Can you disprove it? Have you met his mother? What's the biological father's name? Maybe the Maker just decided to take a turn in the Deep Roads and got misplaced. How did Sandal, a dwarf with no magic or tools, make a rune that froze an ogre? Dagna, brilliant as she is, could only make a rune that destroys armor, and she had some pretty hot custom tools.
You can never prove something does not exist. Remember when they discovered the Coelacanth in the '70s? All the papers said how they'd found a living dinosaur and it was a miracle. Turns out, there's a whole colony of them near Madagascar. The Scots have been sailing with the Loch Ness Monster for how long and no one's seen one that anyone believed, ultimately? A few doors down from where I lived was an old inn George Washington slept in. The well was supposed to be haunted by the ghost of a serving girl, and it turns out to have been swamp gas from rotting potato peelings. I used to cross the street and walk on the other side at dusk and dawn, just in case, you never know. Servants did sometimes fall in the well.