I put this earler in the phrase "reflection completeness": https://sdrinf.com/reflection-completeness ie there are things which stops working when people know about it.

In particular with A/B testing, this means that the initial A/B test is intermingled from at least 3 effects: specifically it measures how the naive population's behavior changes as a function of new functionality being made available. This is heavily, heavily time-dependent; specifically there's a "novelty effect" (early data collection will not be representative to long-term usage patterns); and there's "reflection effect" (once the outcome of the test is widely known, people can change their behavior based on that). Controlling for the first is difficult, but possible; controlling for the second, beyond just "keeping everything secret", is significantly more so, as the timelines for that might be years in length.

I strongly suspect GP was pointing at this timeline factor, and specifically that market engineering, as currently, generally, widely practiced, is grounded on the immediately available signal of "does it increases sales in 2 weeks of A/B test running". Which, given novelty effects, is heavily biased towards "yes"; and these people aren't incentivized (nor have the time/energy) to measure _very_ long-term effects beyond novelty, and reflection period.