In our case, it's to offer the most rapid experience possible. There is no checkout, setup of build, npm install or other things. It's all ready to go immediately. Also we built really specialized views and features for the job. You have immediate feedback out-of-the-box or you can review UI changes graphically by comparing results, to name a few.
This been said, we are working on a CLI to "checkout" the components locally, use your editor of preference but still benefit from everything above.
Specially for Show HN we built a little Hacker News Custom-Element button https://webcomponents.dev/edit/RE957cUuYlJO0DZFJIz3
Happy to answer any questions