Because "people are dumb"? Well, people aren't dumb-dumb but just as you aren't going to get everyone to code, you aren't going to get everyone to understand abstract logical relations (not generally, throughout society, though anything is possible in a single enterprise).

Spreadsheet maintain their dominance in places that they logically don't belong because you will always have a person who got their position, in say a brokerage firm, through social intelligence, language intelligence or "sheer guts". And they will want to be able to manipulate data without training and spreadsheets let them. Heck, we can't replace the Excell interface with a better spreadsheet interface.