My husband bought me the book Shady Characters: The Secret Life of Punctuation for Valentine’s Day. From an interview with the author:
. . . the earliest typewriter keyboards did not have exclamation marks (typists had to type a period, a backspace, and then an apostrophe to simulate one), and the various different dashes—the em, en, figure, and quotation dashes, along with the hyphen—were conflated into a single “hyphen-minus” key that still blights the computer keyboard. Not only that, but many people persist in typing two spaces between sentences because it looked better in the context of a typewriter’s monospaced letters. The typewriter has a lot to answer for!