Intel's Turbo Boost specification only allows for a few seconds of boosting. Of course you can overclock (letting it run longer than stock settings) if you have better cooling or if you won the silicon lottery.
Furthermore, I think the advertised Turbo Boost 3.0 frequency is single-core only. It will not increase all core frequencies to that level unless there is sufficient thermal headroom.
Maybe some of your users block Google Analytics/Mixpanel while not blocking Facebook ads. For example, because they are using the mobile app or because Facebook ads are harder to block...
It had even led to some anomalies where Apple machines were a better price than similar Windows machines.