[antonovka]

... I guess one reason for it is that BSD license put off more developers compared to GPLv2.

No, it was just timing. The AT&T lawsuit cast a palor on the BSDs just when Linux started hitting its stride. By the time the lawsuit was settled, Linux had dominant mindshare.

Same reason why MySQL is popular -- PHP gave it the mindshare. Same reason why PHP is popular -- it was one of the few options available at the time, and by the time better things came along, it was already firmly rooted.