I've used antlr to generate parser for small language used in one project. It's like 100 declarative lines of code. Writing parser by hand would be a much more complicated task.

I didn't really care about diagnostics. It has some, that's enough.

And of course it's easier to maintain declarative grammar description.

My guess is, that it's often used for those kinds of simple grammars without high requirements to impementation. When you need to get things done. Like regex. You might write code to parse a string in a more efficient way, but with regex it's almost always easier. So ANTLR is like regex engine for more complicated inputs.