Weapons... What a topic. I've trained in a number of weapons arts and arts that did some weapons training. I think the main reason to train in any weapon (unless it's part of your job), including modern weapons like firearms, is because it's interesting, fun and may teach you something useful about combat in general. In some cases (looking at you Aikido) they may be a useful tool for teaching the principles, movement and body mechanics utilized by the style.
I got to participate in a small weapons demonstration that my Hapkido instructor put on for the few students who were really interested. He could do amazing things with a large handkerchief that definitely qualified as a flexible weapon. He was super creative with it and used it in a lot of different ways, to block, catch and trap, to increase leverage for throws (after catching a limb with it), as a distraction with a quick snap, and other things I don't even remember at this point, it was awesome! If he hadn't closed his school it was one of the things I really intended to pay private lesson rates to get him to teach me.
He didn't teach it as part of the regular curriculum because he said it took way too long to learn and that adults in America with full time jobs and families and things could get a lot more value out of putting that time into the fundamental empty hand techniques. But he felt that way about all the weapons, he did some great demos with a very short thick stick that I can't remember the name of, the cane and some other things, but he didn't think any of them were worth the time they took to learn for most people.
I would certainly agree that most flexible weapons, especially exotic flexible weapons like the rope dart, are pretty impractical if you're looking for a direct, real world application. I also suspect that very few people teach/train the more exotic ones with anything more than form demonstration in mind. I've never done any real training with any of them, but I wouldn't be surprised if they had some utility at least in some circumstances as a training aid for improving coordination, instilling an understanding of certain principles and that sort of thing. I also used to know a guy who could break a variety of things with the meteor hammer much like the guy does with the pots at ~2:10 in this video:
https://www.youtube.com/watch?v=uhW67MBO8M8
I don't know if it could be used practically in a fight but I wouldn't want to get hit by someone who knew what they were doing with one either!