I think big companies see a lot of opportunity in locations outside of Silicon Valley. If you don't care about the weather in the Bay Area, which is quite pleasant, or the other industries around you (be it for business or for pleasure), then you can get an easier commute and a better house for the same salary, which is appealing to some people. (You can also pay people less, which seems to be a strategy used by companies without any Bay Area locations.)

As for how these offices exist; sometimes the team lead is senior enough to move the project there because they want it to be there, and other times a company is acquired that has offices there and there was no reason to move them. (I think Google got their NYC office by buying DoubleClick, for example.)

But then it's weird to specify a location. Camrose is a town of 18,000 people – why not make it explicitly remote?

Yeah that's a really good point... Is this perhaps one of those hyper specific job postings so that a company can skirt some sort of regulation about hiring immigrants by saying they did a search? but why Apple? And why Camrose...

The next Bend, Oregon!

It all comes down to world-class talent and their willingness to relocate. John Carmack famously joined Oculus without leaving Dallas, TX. I also believe that Chrome's entire V8 team is based out of Aarhus, Denmark due to Lars Bak's desire to move back home.

I think that may have been true at some point, but I believe only the Dart language team is there now. Could definitely be wrong though.

Apple has a number of small offices around the world in addition to their large presence in the Bay Area and Austin.