Why is the software under the Public Beta Program considered confidential? The FAQ page for the Public Beta Program includes the following entry:

Is the public beta software confidential?
Yes, the public beta software is Apple confidential information. Don’t install the public beta software on any systems you don't directly control or that you share with others. Don’t blog, post screen shots, tweet, or publicly post information about the public beta software, and don't discuss the public beta software with or demonstrate it to others who are not in the Apple Beta Software Program. If Apple has publicly disclosed technical information about the public beta software, it is no longer considered confidential.

Why is it considered confidential if it is completely free to enrol in the beta program and anyone with an Apple ID can do it? Is there some kind of weird legal issue or is Apple just reusing some parts of their TOS from other things?
One reason beta software is restricted and considered confidential is that by exposing features could result in revenue recognition issues for the company, which could result in the company refunding money or needing to restate their corporate financials.

Lets say you play with the beta, and are extremely excited to discover that this beta has support for left-handed keyboards. As a big user of left-handed keyboards, you begin tweeting about the support, write blog posts, etc.  Many users decide to purchase new Macs because they too are anticipating left-handed keyboards. However, Apple decides that supporting left-handed keyboards doesn't work well enough, and decide to not ship the support in the golden master release. Customers sue Apple, demanding not only refunds but reparations for lost time because of the "missing" support. The SEC investigates Apple, because they feel Apple may have mislead investors, who anticipated that there would be lots of sales of Macs, partly due to left hand keyboard support....

You get the idea.