They have enough employees to build native apps that run super quick but are still seduced by the web portability argument which, as we all know, is mostly untrue even now and which introduces all kinds of non-deterministic latencies/errors, which cannot all be handled neatly.
To be honest, this is the same in almost all apps that have any more than 10 developers working on them (my estimate!). Death by dependencies and a lack of coherent design.
As someone else said, though, some things like fastmail work OK in the browser so it is possible.
Native software is incredibly difficult to build well.
There are at least 4 platforms they would need to support: Win, Mac, iPhone, and Android.
That's 4 different software engineers at least, just for the frontend.
Then, there's various backend engineers, who could be shared, yes, but not always. Android's weird runtime requirements are bespoke enough that just because the database is written in C++, doesn't mean it's the same C++ database as what the Windows backend would use.
Finally, there's the designers, who end up consolidating all the unique things about each native platform into a common design language so they can have a shared vision on all of the platforms. So engineers end up building UI that works identically on all 4 platforms, and you're basically building a bespoke "browser" at that point.
I have to agree here but I would like to add: every single web app I have ever had to build or was part of building was heavily biased and towards adding more features and exorbitant amounts of tracking that me or the other engineers had to practically beg the product owners to do do perf optimisations or reduce technical debt that accumulates after a couple of years, even with lots of low hanging fruits to pick from.
To be honest, this is the same in almost all apps that have any more than 10 developers working on them (my estimate!). Death by dependencies and a lack of coherent design.
As someone else said, though, some things like fastmail work OK in the browser so it is possible.