Your Questions Answered:
Because those statements are partisan. Including partisans you don't agree with who use deceptive arguments and confusing language. Voters really want information they can trust, they want it to be easily understood, concise, and they don't want to be lectured. Peer statements fit the bill.
They're randomly selected, regular folks, from all across the state--a representative cross section. They're trained in how to evaluate both experts and partisans, and their deliberation is facilitated by disinterested moderators to ensure everyone on the panel is listened to.
It's been shown over and over that ordinary people, given real responsibility, act responsibly. They can understand complicated issues, and collectively make quick, smart, unbiased, non-partisan decisions, and generate new and unexpected ideas. The most important ingredient in good, collective decision making is diversity, not expertise.
In Oregon they're picked by the commission which oversees the panels. But if we do this is California, the panels should be given a say as well. The commission also decided, based on how controversial they are, which initiatives get a panel. And they pick the panel moderator--the group that runs the panels. In Oregon this has been Healthy Democracy. There's a link to their website at the bottom of this web page.
The Oregon law specifies the composition of the commission. One member is chosen by a Republican in the state legislature, one by a Democrat. There are four former panel moderators and four former panelists on the commission. It's not a partisan body.