The limit is imposed by Discourse to ensure that over time, and with many thousands of posts, the URLs—which are derived from the titles—are unique. You can imagine what it would be like to have lots of posts titled “Broken link” or whatever. Meaningful titles are, in most cases, a good thing.
doesn’t the system assign a numerical value to a topic URL as additional identifier like 2560 in case of this one, which i believe is supposed to be unique by design?
True, but check it out: you can delete that number and still get the right thread. It’s just more robust to have unique, descriptive titles, as well as more helpful and useful for scanning threads and search results, etc.