OK, what I see about the top end 600 on Amazon is that "Product Feature" say "Focus-free lens for great shots as close as 2 feet" (looks like 'marketing speak' to me) The "Technical Details" say "Focus range: Fixed focus; 2 feet to infinity" and "Focus system: Fixed focus".
So, why no focus on the 600? A 2 element f/12.9 100mm plastic lens and an integrated flash means you don't need to focus. I'd say years of experience with the consumer market is why there is no focus.
I've got an old 600 (SE with the f4.7 4 element 127mm) - It will focus as close as 3.5 feet - but at f/64 the near end of focus will be a bit closer. I'd feel safe to say this camera was not oriented toward the consumer market.
Oh, by the way - I sold quite a few Polaroid cameras back in the early 70's and some of them were a PITA to focus - the original SX-70 for example had no focusing assistance on the focusing screen (a split image was added quickly) and I heard may complaints about 'unacceptable photos' from a top end camera that used film that was not inexpensive. When you inserted a flash bar the aperture was set to the focus distance - so when you missed you got over or under exposed photos. Ever do the "Big Shot Shuffle"? At least the rangefinder on it was pretty good - and that was fixed focus. Now, people are asking, and even getting, big bucks for them on eBay (I sold quit a few of those back then.) Some of the less expensive had 3 or 4 zone focus - head&sholders, group of people, mountains for example, and if you 'forgot' to focus, you'd get 'unacceptable photos'.
My favorite Polaroid film was 809 - I'm just glad I found my 18-12 processor in the trash - complete with the hand crank - so I won't feel so bad having to put it back there someday...