Closed captions aren't universally available, and live captions are often pretty awful (captions for recorded content are often fairly awful).

I recall seeing interpretters on TV during special broadcasts a lot, but then they were mostly replaced by open captions or (presumably) closed captions as captioning became generally available. I'd guess there's a bigger pool of skilled captioners than skilled interpretters, but it's also a lot easier to find someone on staff who can type fast to caption in a pinch.

All that said, I do see some very special events with interpretters still, and I apprechiate that, even though I don't sign.