This is more of an old web, and because of bad design: keeping state of the app on server, rather than in the browser (or are you referring to limiting open in new tab?).
Tab in browser provides way better user experience than electron app (or native android/ios app). With website you can to mind-blowing things like:
* Open other part of your app in new tab.
* Open other part of your app in new widow, and have time side by side.
* Open external link in new tab, in the same window (OMG!!!).
* I can send link from the web app to someone else.
* Consistent back button.
* Use browser extensions.
* Have cookies (i.e. I am logged out of most of the things in your in-app browser).
Composers are generally thing that are better in apps, but as long as I don't need to compose complex stuff, web app always wins. And if I do, I'll prefer to use native/electron app only for composing, not for consumption.