Because those libraries are intended for scientists rather than programmers.

If you look at code in other languages written by scientists/mathematicians, you'll also see tons of needlessly shortened variables names. Often just x and y.

Reasons vary, part of it is how they think about problems. Holdover from pen and paper research where var names were shortened to one letter to save manual effort. Part is that this community were some of the earliest programmers, when memory was so scarce that you'd want to save every byte, even in the source code.

Python with numpy and all stands out because none of the practical concerns remain, but the culture persists and looks a bit absurd.

i dunno. it's a tradition at this point. i mean, we use indents instead of braces, you may have more important questions to ask

Tbf, typing pandas every time is goofy af.

As I tell my students though, remember that Python was also intended to help people who aren't programmers that use tools that aren't suitable for coding actually accomplish something due to the readily available modules and the ease of acquiring modules that do the things you don't know how to code. You know what supposed to happen though.

They can see it by checking the imports at the top or by ctrl-clicking the shortened symbol (in most editors anyways). These shortening conventions are pretty well-established to be clear to anyone familiar with these libraries and immediately picked up by anyone getting into them.

On the other hand, e.g. complicated matrix operations would be a syntax hell if you had to write numpy in front of ever damn symbol in the expression. They are often syntax hells as they are ;) .