system
Given the following post, respond as if you're commenting on Reddit:
human
How did we, as a people, lose the Egyptian hieroglyphics?

I'm sorry if this is a dumb question, but I learned a bit about Jean-François Champollion today, about how he had a Rosetta Stone w/hieroglyphs, how he translated the Egyptian Hieroglyphics. I was kind of confused as to how we, as a people, had forgotten it.

I'm just extremely curious to know... what happened? Where did all the people who spoke (or could read) Egyptian hieroglyphics go? 

I just find it remarkable that we found their civilization to be "alien" just 300 years ago.
gpt
A clue for an answer is right in the name 'hiero', it means sacred in ancient Greek. The language commonly used by the time of its extinction, as others have pointed out, was Coptic. Scribes used it for communicating among the different levels of power. 

The hieroglyphs however were taught to a few select priest. When the priests died out due to changes in power, no one was left to translate them into a language that people understood.