Why did the original Unix versions suddenly become open source/free? It seems odd that AT&T and Bell Labs would let something like an operating system become moldable and resellable with all of the funtionality that operating systems hold, especially with the small amount of them back then. I know that they allowed it to become open source, but I can't find out why they did.
From The Art of Unix Programming (emphasis added):
After the  paper, research labs and universities all over the world clamored for the chance to try out Unix themselves. Under a 1958 consent decree in settlement of an antitrust case, AT&T (the parent organization of Bell Labs) had been forbidden from entering the computer business. Unix could not, therefore, be turned into a product; indeed, under the terms of the consent decree, Bell Labs was required to license its nontelephone technology to anyone who asked. Ken Thompson quietly began answering requests by shipping out tapes and disk packs — each, according to legend, with a note signed “love, ken”.
There is much more relevant information in that chapter; its title is "Origins and History of Unix, 1969-1995". Highly recommended reading (along with the rest of the book!) :)
AT&T had been forced to open source UNIX, as initially AT&T, SUN, IBM, HP, Tandem, Berkeley Univ, Digital were contributors in developing the UNIX kernel actually developed by Ken Thomson and team.
After UNIX became more mature, the source code had to be shared between the above said companies as they wanted to file their own patents and so you see UNIX tweaked to each of their own patented RISC hardware and so came out the UNIX patented OS's like IBM-AIX, SUN-Solaris, HP HP-UX, Digital Tru64 etc... and that is the reason you see the core commands similar. However Berkeley Univ had developed UNIX close to x86 hardware and called its a BSD (FreeBSD, OpenBSD, TrueBSD) etc...