Sites that try to trick users into signing up to browser notification spam are increasingly becoming a method used to promote unwanted extensions, fake software, adware bundles, adult sites, and scam sites. The problem is that many users may have no idea how these notifications are appearing and will continue to receive them until they remove the subscription. Thankfully, removing sites that you are subscribed to is fairly easy. You can check for and remove subscriptions by going into your browser’s settings to remove them in Chrome or Firefox.
Source: https://www.bleepingcomputer.com/news/security/sites-trick-users-into-subscribing-to-browser-notification-spam/