It is odd that you've long been able to buy a cellular iPad but not a cellular MacBook.
Perhaps people who buy a MacBook are likely to have an iPhone in their pocket that will function as a hotspot and iPads are much more often used by people who are otherwise outside of Apple's ecosystem?
If you are signed into the same Apple account on your iPhone and your MacBook, the iPhone shows up as a WiFi network option you can select without having to do any additional configuration.
It's one of those "It just works" continuity features, like sharing the clipboard between your Mac and iPhone without needing to configure anything.
