Even in the beta book, the NPCs weren't 'limited' to the 8 races. The NPCs includes Aqualish, Gamorrean, Mon Calamari, Barabel, Defel, Sullustan, and a Hutt. I feel like there was a Quarren, too, but I couldn't find it on a quick scan.
So there's already at least 7 more races already in the game, even they aren't worked up as player character templates.
While those are fine for NPCs, there is the issue of these not being "worked up" for usage as PC races. And for most of them, there's no mechanical difference between being a Aqualish, a Barabel, a Gamorrean, or a Sullustan. Mon Cal and Defel have an Abilities entry that separates them a bit, but that's it. Cyril and I used what few mechanical tidbits there were for the Unofficial Species Menagerie, and we wound up having to create a lot of it from scratch.
And while some folks might be fine and peachy with coming up with their own versions, not everyone is, and some GMs, new and veteran alike, prefer to keep anyone's homebrew material as far from their gaming table as possible no matter who wrote it.
I am kinda saddened that FFG won't be going past the initial 8 in the corebook. I doubt we'll see anything like WotC's Alien Anthology supplements for their OCR/RCR product line, but rather a handful of new PC-ready/viable races in each supplement. And I'd be greatly surpised if we don't get at least a handful of new races in the Age of Rebellion and Force & Destiny books; probably safe to figure that Droids, Twi'leks, and Wookies are going to show up in at least one of those other corebooks, with Humans appearing in both.