The steady expansion of character set sizes also had a great deal to do with it.  The various 6-bit character sets were fine as long as the industry was okay with English-only SHOUTING.  When that was outgrown, 7-bit ASCII and 8-bit EBCDIC on multiple-of-6 word sizes (as were found on the big-endian DEC machines up to the PDP-10) were annoying to use.

On the 12-bit PDP-8, where I cut my teeth, ASCII was stored as

HHHHAAAAAAAA followed by LLLLBBBBBBBB, where the As represent the first character, the Bs the second, and the Hs and Ls the third.  Padding was done with NUL, which meant that, for example, the TTY driver simply filled its read buffer with 0000AAAAAAAA 0000BBBBBBBB, which made rubout handling much simpler.  Textual programs reading from it would already be set up to ignore NULs.

On the 36-bit PDP-10, things were better: the sign bit was mostly ignored and five 7-bit ASCII characters were packed into each word, again with NUL padding.  (Line editors turned on the sign bit to indicate that this word held an explicit ASCII line number.)

John Cowan          http://vrici.lojban.org/~cowan        cowan@ccil.org
Original line from The Warrior's Apprentice by Lois McMaster Bujold:
"Only on Barrayar would pulling a loaded needler start a stampede toward one."
English-to-Russian-to-English mangling thereof: "Only on Barrayar you risk to
lose support instead of finding it when you threat with the charged weapon."