It's easy? It works? It feels like HTML? No build steps? No JSON? The primary documentation fits is a single page? Most common patterns (i.e. polling, and then stopping if necessary) are built-in? The entire dev experience is focused on a single application (backend) as opposed to writing a backend and a separate frontend project? Simply replacing HTML fragments is conceptually simpler than maintaining a shadow DOM? It embraces web standards/APIs (see client validation discussion above)?

Here's polling in Svelte: https://stackoverflow.com/questions/61391174/how-to-do-polli...

and in HTMX:

  hx-trigger="every 2s"

https://htmx.org/docs/#polling

Maybe Svelte has an easier way, but Google isn't directing me straight to it, which is all part of the "easy to learn" aspect.