I'm not sure that this actually suppressed wages that much. Oligopolies only work when nearly everyone is in on it. If you have too many 'cheaters' than the cartel can't control the price.
There were a lot of tech companies that weren't in on it. They were still poaching employees, and employees were leaving to do their own start-ups.
No in industrys the big players tend to set the going rate for pay increases. HR use surveys of wages to set compensation quanta and if all the big players he suppressed wages this will effect the surveys and hence every one's compensation.
I think that there are other wage setting mechanisms that you're neglecting. An employer that pays above the market rate can get better talent. An employee can ask for more pay. They can leave for a job that pays more. ect.
And I think you misunderstand how big companys set wages - they use some very secretive "surveys" which they do not share with the employees to set the quanta for pay increases.
