Compared to fixing existing bugs ?
I'm assuming that MS has decent code quality standards here.
Especially when dealing with large and complex spreadsheets.
Previous discussion here: https://news.ycombinator.com/item?id=17300893
Would be interesting why they moved from this approach to React native.
Here's the reddit comment  with more details (copy pasted the text of that comment here):
> Hi there!!! Original Tweeter here! I'm Sean and I'm a Program Manager at Microsoft working on Microsoft Edge and Edge Dev Tools!
> Feel free to ask anything else! It's the least I can do for tweeting some pretty unclear messaging.