Because some people will be playing your game on itch, some on ludum, some will download, and the one very important button that is needed for your core mechanic will be forgotten. It happens every jam that I play some game and can't figure why it is so bad until I notice that there's some action I can do that was only referenced at itch.io.

• If you update you build you WILL forget to update control at some place

• Don't you want you game to be preserved for the future players? If you make a nice game some people may notice it way after the jam and maybe download it to play later. Why would you want them to no know control then...

Just enabling some UI on top of a game when pressing F1/Esc is enough. Or show them in game menu/start screen. Show them in game somewhere, please :)