>Implement something like that without a framework and only plain js with dozens of fields having dependencies on each other, good luck :)
I just implemented a complete spreadsheet solution inspired by Airtable (sticky header and columns, column resizing, virtual scrolling, row selection, cell selection, cell editing, a few cell types) in approximately 500 lines of vanilla JS. No virtual DOM, no reactive data library, no framework. Just direct DOM manipulations. It performs great and is pretty easy to understand and extend.
For now, the reactive "field dependency" problem is just solved by re-rendering the entire spreadsheet when a cell is updated (really just re-rendering the visible rows, because of virtual scrolling). The state management is just not that complicated.
I suggest this sort of project as an exercise if you've found yourself engrossed by this or that front-end framework. My go-to front-end frameworks for the past few years have been Mithril.js and Vue, but they really would have been a major hindrance in this case. I can't imagine Svelte or Solid.js or whatever being any better...
Re implementing custom app with its business rules that was buried in excel sheet is a different thing. People don't want to buy excel in a browser, because they can have that already, they want their custom logic and in a way it works in excel.
Take for example excel and if you change value in one cell you get all calculations in sheet updated automatically.
Implement something like that without a framework and only plain js with dozens of fields having dependencies on each other, good luck :)
Implement something like that with cute "recalculate" button on the bottom of 3 screen scroll and no one will use your solution.