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Probably the same reason they're using Ubuntu and Chrome: the alternatives, while free, aren't fashionable enough.

Except Ubuntu and Chrome are both really good products while still being fashionable.

I'd use Sublime any day of the week over Gedit even if it wasn't "cool"

Gedit is pretty bare-bones and not really a programmers editor despite a few features in that direction.

Geany, on the other hand is everything a beginner needs and without proprietary concerns.