The practice lap time conundrum

So interesting that people like Cooper and Barcia are able to turn substantially faster lap times (albeit on a pretty wet track) and things can be so different when the gate drops.

I’m using these two as an example but this is the case almost weekly. Someone like Baggett can put down a lap time 1 second faster than Tomac but Eli dominates the race.

Is this an age old case of things just being flat out different when the gate drops verse practice? Does Tomac make less effort in an attempt to conserve energy during practice? Also not just Tomac, many of the top guys.