Showing gameplay would be pointless because 99% of the gameplay is in player's head, analyzing the code, maybe even writing some down on paper. If you just look at the screen, it doesn't make much sense.

Here, try looking at this gameplay video:

https://www.youtube.com/watch?v=u4RskXHDLzo&t=183s

It's hard to pick any point in that 75 minute video that would be a good trailer material. There's nothing visually spectacular except some static ASCII art and there's no surprise mechanics that would draw attention. The game itself isn't about ASCII art anyway, so having that in the trailer wouldn't make you learn much.

But then again, it isn't a game for everyone. It's for people who are into hacking, computer internals, binary/hexadecimal numbers or assembly/machine language.