I think it is a matter of target metric. You can optimize just for click-through/watch time (short term reward), but you can also target a composite of that and

I think it is a matter of target metric. You can optimize just for click-through/watch time (short term reward), but you can also target a composite of that and quality/trustworthiness (long term reward). YouTube seems to mostly optimize the former, while search seems to compromise between both.