The answer to this can be found in Chapter 13. Specifically, it can be found on page 248 in the paperback edition of the book. On this page, Diamond is discussing why societies accept some inventions and start to use them while they refuse to use other inventions. Non-traditional keyboards are something that our society, at least, has so far refused to accept.
QWERTY keyboards were specifically devised to slow people down as they typed. This was because early mechanical typewriters became jammed if a person typed too quickly. Of course, this is no longer a problem, so why not change to keyboards that would help us to type more quickly?
Diamond says that this is because inventions fail to be accepted if they are opposed by “vested interests.” If a group of people has an incentive to keep things the way they are, they will oppose the new inventions. Diamond argues that all of us who have learned to type on QWERTY keyboards, along with “typing teachers, typewriter and computer salespeople, and manufacturers” all have a reason to resist change.
Thus, we still use inefficient keyboards, Diamond says, because too many people have a stake in keeping them around.