Why café menus have typos

It's always been a mystery to me why so many shop signs and café menus have glaring typos and spelling mistakes.  Surely the core job requirement for a printer or signmakers is basic grammer and owning a dictionary? (See, I don't even expect them to be able to spell, owning a dictionary would be good enough).

Well, here in Walthamstow I've discovered what I suspect is the source of at least some of these  howlers.  Would you buy a sign from this company...?

Stu ;-)

ps In case you can't see it - apostrophe abuse...