This comment is getting downvoted but if it's true, it's absolutely a good point. They are optimizing for what is inherently slower: loading JS in the client before anything can be seen or interacted with, rather than rendering HTML and forms so one doesn't have to wait for JS to compile and execute (and all the tracking bloat that comes with it).

It's a progressive web app. This means users shouldn't have to wait for JS download or compilation on repeat visits.

It is not true, the slow part of web applications is loading over the network, server side rendering puts a dependency on the network and is therefore vastly slower.

With service workers and client side storage you can get to display at least a shell, sometimes the entire UI without touching the network. It is a lot faster

Where do you think that JS in a web page comes from? Not from the network?

Service workers are a cache (and background process), and you still have to consider cache misses. Even if you have a giant JS app and cache it, users still have to download all the JS to actually work offline no matter what.

I don't know why my comment is getting downvoted. I was just making an observation after looking at the source.