But those are the apps themselves. This is about the WhatsApp Web protocol which allows you to use WhatsApp from a browser window by pairing it with a live session on your phone. Since the API endpoint are their own servers and the client is literally just a website, they can update whenever they want however much they want.

One of the things that has repeatedly pushed me off WhatsApp has been their very aggressive stance on this: I've several times stopped using it because "you need to update your app or this will all stop working in 7 days" and I've not been in the mood for jiggling the apps round on my tiny phone to be able to perform that update: the 7 days has passed, and I'm off WhatsApp again until such time as I "need" it.