This is because about 80%-90% of the time, employers (and even more, recruiters) aren't looking at all at any of your intrinsic traits, but rather at proxies, e.g. where you went to school, who you worked for.. and how long you worked there.
That is to say, to a large extent their logic goes like this: "I don't have time to parse all of this candidate X's attributes and traits; but I can see that entity E (school,employer) has conveyed the following attributes {a1,a2..} to candidate X in the recent past. So as a matter of expediency, and to get make some headway this inbox of resumes before I need to get coffee again, I'll just X++ or X-- accordingly."
And it also happens that one of the must highly valued attributes they have is whether the candidate was recently (or even better, is currently) employed by some company they consider to be cool (by whatever criteria).
Of course, it's perfectly fair to say you wouldn't want to work for an employer with such a shallow way of looking at the world... and that anyone who's willing to just close their eyes, and look at the real you not only won't ding you for taking off a year to live in a squat in Barcelona with your hot girlfriend, work at a coffeeshop, and not only start to learn from scratch, but make commits to the source tree to some emerging language Y that's decades ahead of its time, albeit with precisely zero value in the current job market... but might even find you a potentially much more valuable, well-rounded candidate for having done so.
But the vast majority just don't think that way, course.
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