It's also a story about technical people who have options. If Apple's standards for their network were so exacting and impressive, it is pretty unlikely that they had anyone just clinging to the job because they didn't have much hope of finding another one.
If you are already considered good enough with the existing tech that unemployment isn't a serious concern; and your current employer is specifically denying you the opportunity to be part of the cool new tech, why would that inspire you to stay with them?
You can get real hotshots, if the project is interesting and/or the money is good(or the stock options are risky but have the possibility of being really, really, good); and you can usually find people to work with a given system, no matter how legacy, weird, or unpleasant, if the money is good enough; and you can also get people who are unambitious and pretty easy to keep happy; but getting all of those simultaneously is much, much, less likely, if possible at all.
I don't doubt that Apple was able to hire a new networking team; they can certainly afford it; but telling people "No, it is going to be your job to maintain this legacy system and we aren't going to touch the cool new thing" is not exactly a motivational speech.