Whenever Magic: The Gathering goes all in on a hyper-specific region or expansion, they tend to go all in.
Everything from the creatures to the art to the lore are roped in the theme, making places like Innistrad (for example) all the more spooky. Sometimes it even trickles down to the nitty gritty. That's where hieroglyphics kicks in.
Well, almost kicked in.
In 2017, MTG developers decided to do yet another top-down set, meaning that a theme was thought up first with the rest of the set following. The theme thought up? Ancient Egypt, because it wasn't really done before. The name? Amonkhet. It just wouldn't be a new magic set or expansion name if it doesn't sound like it could also be a themed Six Flags roller coaster
Because of the whole 'Ancient Egyptian tomb' bit of history and importance of death in Ancient Egypt, many cards were designed to be used from the graveyard. As such, they also introduced mechanics to make it easier. Deserts, jackals, curses, and other special card types now had special Egyptian mechanics like embalm, in which a creature in the graveyard can become a tokened creature of sorts.
But some cut mechanics would have taken it further.
Mummify almost became one, but it was soon cut for being too similar to other mechanics. And then there was hieroglyphics.
Hieroglyphics would have been applied to things that would be found in archaeological digs. Activated from the graveyard, paying two generic mana would bring it back as well as another card. It was rather simple and effective.
As Mark Rosewater put it "You dug them up."
However, problems soon arose in, where else, playtesting. Unlike most scrapped mechanics, it was actually working. But An upcoming expansion, Shadows over Innistrad, needed some mechanics and had a similar one going for it - Investigate.
"The flavor of hieroglyphics was pretty cool. If you dug them up out of the grave, you could learn things from them," added Rosewater. "The set needed a mana-smoothing mechanic, so I was pretty sure I'd hit pay dirt. Unfortunately, at about the same time in development, investigate was created for Shadows over Innistrad. The two mechanics aren't exactly the same, but they're similar enough that it didn't make sense to have them both in Standard at the same time."
Basically it was a choice over which heavily themed set would win out, and it wasn't Amonkhet.
Still, most scrapped things in Magic don't always have such a happy ending. Hieroglyphics does...through being completely as another mechanic overall.
Of course, that doesn't mean that WotC won't "dig up" this mechanic at some point in the future.