This cartel had 4 members. With all the Silicon Valley tech companies, it's a little hard to see how this would be successful at holding down compensation. In any case, cartels have a historical reputation of being unworkable without laws being passed to force conformance. The problem for the cartel members is they have large incentives to cheat on the agreement. Probably the most famous cartel is OPEC. "Jeff Colgan…
Most companies base salaries on the "market rate." The rate is effectively set by the largest companies. So when the largest companies band together to keep the market rate down, it keeps them down across the entire industry. Even in other cites and states. Did some small companies pay more. Sure, but these smaller companies had a very limited number of openings. Many companies would claim to be not as big as google, so they would pay less.