They don't. A large number of them don't even care. Some even click on all of the "allow this site to send you notifications" and then proceed to get spammed by hundreds of notifications on their phone/PC. And don't mind it.
You are very right, though it's difficult for those of us here to imagine it. 20 years ago, people would browse the Web through a 11-inch by 4 inch slit because all the adware toolbars had nearly occluded the whole viewport. Today most of the webpages themselves look like that without an adblocker and most people just tolerate it. And even click the ads!
