You can already attach ship to ship using towing beam, but grappling hook would be personal item that helps you get onto a target ship in certain range (like lifeline but you choose when to use it and it doesn't stun you).
There was a hook in Worlds Adrift and it was probably the best part of the game. Traversing terrain was so much fun when you learnt how to use it properly. You can still try it in island creator.
But it turned pvp into zerg fest. It was extremely hard to get hostile players off your ship since they could swing around and avoid your bullets while damaging your ship, so whoever had more players would win. Devs had to add ability to your ship to detach all hooks from your ship and make it immune to hooks for a period of time when you decided to trigger it.