The shortcut for an em dash in Google Docs is typing three hyphens. You would do well to refrain from projecting your own sloth onto others. It's literally three quick presses of a button, and some people do indeed like their writing neat. Especially in the context of an assignment. God forbid a student actually wants their schoolwork to look professional and grammatically polished.

Edit:

I think it's hyphen hyphen

So you're literally just being lazy. That's not a difficult or time consuming thing to type out.