'Twas brillig, and the slithy toves did gyre and gimble in the wabe

That would be a sensible reason (and I recall LJ do such a thing), but the Javascript just submits the password in the clear. The sole purpose of the Javascript is to do the login via AJAX.

There is fallback support for Javascript being disabled (via noscript tags and an actual action for the form to submit to). So it'd probably work on the Kindle if I disabled Javascript, but that's not something I should have to do.