Because web security has a lot of legacy crap. Such as cookies. Oh you added Domain=foo.com to your cookie? Now marketingvibecodedapp.foo.com can access the coo

Because web security has a lot of legacy crap. Such as cookies. Oh you added Domain=foo.com to your cookie? Now marketingvibecodedapp.foo.com can access the cookie from your main domain. What do you mean you thought adding the domain field restricts the cookie to just that domain? Lol no, it's the exact opposite, gotcha, dumbass.