Games would go on sale for example 50% off and people would buy them. Then they would have a flash sale for 90% off. People who bought the game for 50% off then refunded and bought it at 90% off. This resulted in lots of refunds steam had to process. Since they couldn’t get rid of refunding games they got rid of flash sales.
There have been a few videos by hardware reviewers to address the sample size concern. Gamers Nexus tested 3 different CPU models with 20+ CPUs each and found that the biggest variance from lowest to highest performance was under 4% while performance variance in most cases was about 2%
https://www.youtube.com/watch?v=PUeZQ3pky-w
The way CPU manufacturing and binning are done means that cpus in particular will have very minor differences within the same model number.