Broadcom is notorious for demanding NDAs for their datasheets, completely pointlessly. I've also heard of companies demanding their parts be redacted on schematics if published, even more ridiculously, though as far as I know Broadcom isn't one of them (I've seen public schematics with Broadcom parts).

Still, from what I've heard of Broadcom specifically, they're pathologically secretive with their documentation unless some star customer dangles enough money in front of them. rpi.org certainly fits that description. So I don't really buy this excuse for rpi here.

In reality, I suspect it's more the fact that rpi.org was started by ex-Broadcom engineers and they brought their culture of secrecy with them.