The problem with a website is your cookies get deleted every once in a while. This is is inconvenient since you have to re login. Also, push notifications for a regular website isn't great (pwas might be better?)
Cookies get deleted when you explicitly delete them (most users don't know how to do that), or when you've set them to expire (which can decades into the future), or when you break your own code (which should be never).
Cookies should be set to session not a date. Many sites like HN don't do that presumably for convenience. I assume most social media sites set a date though.
