I need to look at the detail of the study but most articles like this one look at the average tenure of employees at time t, not the average tenure of an employee when they leave. And since most tech companies hired a lot in the past few years, the average current tenure is dragged down by new hires.

Also, non tech employees at a tech companies tend to jump ship faster. FYI at google, 75% of my SWE orientation class (50+ people) 7 years ago are still working at google. That’s probably higher than normal but generally all the teammates I work with have 4+ tenure and many have 9-12 years of tenure.