* Why is this practice common in Haskell

Here are some guesses:

1. It's common in papers. However, papers and libraries are quite
different. The former usually build up a small vocabulary and having
short names is a big win. Papers rarely make use of the module system
at all. The latter are included as pieces of large programs and their
names need to be adjusted accordingly.

2. It's the default. You have to add "qualified" to all your imports
to make them qualified. In most language imports are qualified by
default. I think the latter would have been a better choice but we
have to live with the current design so bite the bullet and add those
qualified keywords to your imports.

3. Lack of common interfaces. An example would be two different set
implementations that essentially have the same interface but since
there is no explicitly shared interface, defined using a type class,
you sometimes end up with different names. The lack of type families
might explain why e.g. collection classes don't share interfaces.

4. Haskell is a very expressive language. You can often write a whole
function definition on one line! Adding those module qualifications
makes your code slightly longer and it might just break your beautiful
one liner into two lines.