Source: https://meta.stackoverflow.com/questions/424383/why-is-stack-overflow-asking-me-constantly-about-cookies
You can blame Europe and their GDPR compliance. The same Europe that wants to censor the web was once worried about people’s privacy and came up with rules that all websites visited by Europeanors have to follow and that included being able to opt out of some cookies. It seems they can’t or won’t allow a cookie to be set that keeps your cookie preferences so you end up having to choose your preferences on every visit.
I always just hit necessary only on stackexchange. That and close the stupid google sign in popup in the upper right.