I can’t speak to the general case, but let me answer why I picked the web app route in this particular case.

This was/is my reality:

1. I want access to my space from my laptop (mac), phone (iPhone) and tablet (iPad) and browny points for my Boox e-reader (Android) and even more browny points for just having access from any random computer in the world (with a web browser)
2. I have a full-time job, and this would just be a hobby project
3. I have been doing (or been involved in) web development for 25 years

What are my options? I could go native and develop this either as a native iOS app and Mac app, and then do an Android app because why not. This is hypothetically possible, but would mean that 2 years in I’d probably not be anywhere near the functionality that SB has today.

I could go with a cross-platform stack like react-native or Flutter. This would have been an option, I suppose, but neither of those stacks I fully trust in terms of long-term viability yet. And RN is not really built for desktop apps.

Another part of the reality: CodeMirror exists (https://codemirror.net/). This is an amazing piece of engineering that took years to build, it’s a pretty amazing code editor that is very extensible and… it’s a web thing. Having to implement this natively would likely literally take me years.

So I decided on the web app approach. I’ve had native wrappers (Electron and one for mobile apps) along the way, but ultimately removed them because they take too much time to maintain and test, and I’m just a one person army with a few hours available here and there. PWA support is pretty nice these days and gives you a reasonable experience at a reasonable development cost. It’s a good trade off.

Would I make different choices given infinite time and resources? Absolutely, but you know… reality.

This is my story and it doesn’t apply to everybody, but likely other projects have similar reasons.