I get that these are general purpose tools with a lot of use cases, but some real quick examples of "this is a good use case" and "this is a bad use case, maybe prefer SQL/nosql/quasisql/hadoop/a CSV file and sed" would be really helpful, please.
Programming language documentation doesn't all start with "programming languages are used to direct computers to do things"; it is assumed the target audience knows that. Database documentation similarly doesn't start out with discussing what it means to store and access data and why you'd want to do that.
It's always hard to know where to draw this line, and the early iterations of a new idea really do need to put more time into describing what they are from first principles.
I remember this from the early days of "NoSQL" databases. They spilled lots of ink on what they even were trying to do and why.
But in my view this isn't one of those times. I think "DataFrames" are well within a "lingua franca" that is reasonable to expect the audience of this kind of tool to understand. This is not an early iteration of a concept that is not widely familiar, it is an iteration of an old, mature, and foundational concept with essentially universal penetration in the field where it is relevant.
Having said all that, I came across this "what is mysql" documentation[0] which does explain what a relational database is for. It's not the main entry point to the docs, but yeah, sure, it's useful to put that somewhere!
0: https://dev.mysql.com/doc/refman/8.0/en/what-is-mysql.html
On the other hand, how can you become a target user if you don't know that a product category exists?
If you have the problem "I want to analyze a bunch of tabular data", you'll start researching and asking around about it, and you'll quickly discover a few things: 1. people do this with (usually columnar / "OLAP") sql query interfaces, 2. people usually end up augmenting that with some in memory analyses in a general purpose programming environment, 3. people often choose R or python for this, 4. both of those languages lean heavily on a concept they both call "data frames", 5. in python, this is most commonly done using the pandas library, which is pervasive in the python data science / engineering world.
Once you've gotten to that point, you'll be primed for new solutions to the new problems you now have, one of which is that pandas is old and pretty creaky and does some things in awkward and suboptimal ways that can be greatly improved upon with new iterations of the concept, like polars.
But if you don't have these problems, then the solution won't make much sense.