Why didn't they take a raven with them?

I think it was in the show, too. He ordered Sam to send the ravens, but something happened before he was able to.

😂 That'd explain a lot!

... But I don't think so. Maesters typically don't like magic.

The ravens are not magical. They don't tell a raven where to fly, each raven will only fly to one place. That's why they have to keep a lot of ravens and they are each imprinted with ONE location- major castles and forts. They showed the cages once and they are labeled with all the castle names. So a Kings Landing raven will only fly to Kings Landing. A Dragonstone raven will only fly to Dragonstone, etc. And once it gets to it's destination, they can't send the same raven back with a reply because it's not imprinted on the place it came from , it's only imprinted with one destination , which is the place it was raised.

So like you raise a flock of ravens at one castle , lets say Winterfell, they get imprinted there, and then send them out in cages on wagons and ships to all the other castles. So then all the other castles use those ravens to send messages to Winterfell.
It's also why you can send a raven from North of the wall , or from a ship, or the middle of a forest, but you can't receive ravens there. Because there are no ravens imprinted with that location.