The mistake is "the grid". The spreadsheet as a way to allow IT-illiterate to do stuff on a desktop is a mistake.
Yes, we do need some kind of tabular data UIs but SMALL UIs elements, not the base of the UI. Beside that the obscene "wrapping" of Python to make it "user-safe" makes also it next to useless.
A less ugly approach to tabular UIs is the one from R-Studio, while it's limited, another is org-mode tables while again they are limited in UI terms. Both are a bit better than Jupyter REPL model witch is itself far better than a spreadsheet.
At a basic level because we almost never have to deal with pure tabular data without anything else. A spreadsheet was designed to deal with pure data, even without a note. Than since in the real world we need notes, titles, small bits of text etc spreadsheets devs add styling and the nightmare began, a grid to deal with data, but also formatting styles, people to manually tweak column and row width and height, add colors, ... all manually of course. Then overflowing text. At a certain point in time Microsoft decide to allow "integration", witch is not integration at all (OLE, with the ability in this case to insert a spreadsheet inside a text document) and the nightmare keeps extending.
The most basic error is WYSIWYG, it can work to a certain extent, like CAD systems, where you can "free draw" something but any line have defined parameters, we have snap concept to state a line is connected to another, defined properties like length and so on so in the end we have "a model", a free draw witch is also a set of data constrained/in relation with a set of functions but in general it's a nightmare. The second basic error is try to compensate the lack of integration, a system designed for commercial purpose in witch any software is a standalone closed product, by adding features that in theory can only grow to create "the complete thing" witch is an impossible goal and makes in practice just bloatware. The third basic error is consider users a bunch of imbeciles who can only learn a thing "click around on some pictogram and enter text like a chimp plunging fingers slow and hard". If you craft something simple and explain the principle behind people will learn and act. Oh, of course you need a bit of INITIAL training but after it they are ready, like teaching how to fish vs giving a fish to a hungry person. Oh, of course commercially hungry people are nice, they are tied to the vendor and they keep spending, being locked where they are, but locked people are not productive, like slaves do not work well compared to free employees.
That's the spreadsheet mistakes and modern IT mistake in general: the will to keep users ignorant while trying to made them productive anyway instead of teaching them, giving them powerful tools. It's not transforming anyone in an engineer, it's just the same concept of schooling for all, ensuring anyone have a minimum culture needed to be a Citizen in a society.
A professional mechanic certainly not, someone who know the car enough to understand why there is a strange noise from the beaks and a kind of hiss from the belt (in an ICE) yes. Not differently from why I want any adult know enough about drains, sewers to understand why not throwing pads in the WC or why I want anyone knowing enough about food to understand why we cook certain foods and we eat others raw.
It's a classic concept: the general and generic culture ANY Citizen should possess, learnt back at school. Without that we are all robots, beasts pastured by the shepherd unable to comprehend why we do something instead of something else and so unable to decide peers between peers in a Democracy. Anyone have his/her own specialization, but we must still know a bit of anything at a high level, but still enough to understand if something could be logic/true or not.
A society that work, evolve positively is formed of Citizens not meat-based robot able only to do 1/4 turn of a wrench. People who crack their windshield in the winter, defrosting it with boiling water, others left without fuel at sea in the summer and so on should not be a thing. A child is a child, an adult MUST BE an adult, a Citizen. It's about time to say "if you have to use a computer, a desktop, to work you MUST know it enough, not being just able to click around not even knowing what is a file". In the west world due to such evolution we are unable to do almost anything these days, we have lost much of our best scientific and industrial power because of such idea.
Yes, we do need some kind of tabular data UIs but SMALL UIs elements, not the base of the UI. Beside that the obscene "wrapping" of Python to make it "user-safe" makes also it next to useless.
A less ugly approach to tabular UIs is the one from R-Studio, while it's limited, another is org-mode tables while again they are limited in UI terms. Both are a bit better than Jupyter REPL model witch is itself far better than a spreadsheet.