Essentially, when browsers started to initially implement toggles to block third party cookies more than a decade ago, advertisers in response pressured website hosts to mark their cookies as “essential/required” (AKA forced cookies). You will not get the same revenue as a website host if you do not play ball with this, and some go even a step further by routing/disguising their cookies through trusted domains (google, amazon, etc…) to mask the “true source” , in an attempt to mitigate detection from basic browser filters.

Ublock Origin and the like are pretty good at catching most of them through crowdsourced lists though.