FOSS came into existence during this time because computers and the internet became available, not because it was a specific economic situation.
> If you had a decent job during that time, then the future looked bright and you didn't think twice about giving some of your leisure time away for free.
This seems like rewriting history. Tech salaries today are higher than they were back then. There was even a whole lawsuit against companies caught suppressing wages during that time. Tech compensation went up significantly after the period you cited.