It's a tool. It's not a human. A line number works great for humans. Today, they're terrible for LLMs.
I can choose to use a screwdriver to hammer in a nail and complain about how useless screwdrivers are. Or I can realize when and how to use it.
We (including marketing & execs) have made a huge mistake in anthropomorphizing these things, because then we stop treating them like tools that have specific use cases to be used in certain ways, and more like smart humans that don't need that.
Maybe one day they'll be there, but today they are screwdrivers. That doesn't make them useless.
Check the whole ecosystem around editors, grep tools, debuggers, linting and build tools. One common thing about all of this is line (and column) number so you can integrate them together if you want to automate stuff. Like jumping to errors (quickfix in vim,…), search all files and jump to the occurrences (grep mode in emacs,…), etc…
a line number is plenty of context - it's directly translatable into a range of bytes/characters in the file