Honest question: Where do people think those cookie banners come from? Because, they aren't a dark pattern. They aren't a sneaky way to try to juice your engagement numbers. They didn't show up everywhere because growth hackers started getting jealous of the other guy's cookie banner. They are literally required by law, or at least many lawyers interpret the law in that way. The designers at my work really didn't wan…
Cookie banners are only really required if you're doing things like using them for "personalizing ads" and the like. If your cookies just there to check if you're logged in and other essential functions, you don't need a banner.
I'd guess the thinking is "Well, I don't really understand those requirements and it's hard to be sure if we meet them, safest just to put the banner on." And "Well, if we don't need it, how come all these OTHER sites have it? You really think they're all wrong and you're right? What, are you a fancy pants lawyer now?"
"Cover your ass" is the main driving force of most of America.