You may have been in the heavy ads group from some sort of A/B experiment on how the number of ads they show affects engagement. YouTube runs these sorts of exp

You may have been in the heavy ads group from some sort of A/B experiment on how the number of ads they show affects engagement. YouTube runs these sorts of experiments all the time to improve "metrics". I've heard that there's even a long-running "control group" that doesn't get ads on YouTube.