Because I've noticed that my general happiness in life is inversely proportional to the time I spend writing bash.

Python works better on windows than bash does. This is for less technical people who may not want to install and maintain cygwin.

Are you really asking why one wouldn't "read PDF and word documents", "parse CSV and json files" or "manipulate images" in bash?

You... probably aren't the book's intended audience. :)

But seriously, Python makes easy things easy. In bash, just to extract a substring you need to do something like echo someletters_12345_moreleters.ext | cut -d'_' -f 2 That's not very beginner-friendly.

Bash is great for really simple things, like renaming a load of files in a loop but the bigger the scrip gets the more I would move towards Python. (i.e. more than one nested loop). Plus somethings are horrendous to remember the syntax for, like capturing a regular expression group.

(My personal choice would probably be Perl for many of the tasks, though I would point beginners to Python for its readability).

Bash has more "gotchas" to remember, and tends to be less readable.

Because if you're going to learn a programming language to automate the boring stuff, Python will be easier and take you farther.