It was a jack of all trades. It produced web content through the shockwave player, was extremely popular for interactive CDs, and had a strong presence in kiosks and installation art with its ability to easily interact with hardware. You could embed pictures, audio, videos, flash content, 3d content, and other director movies. And if you're targeting windows, even active X controls. And what it couldn't do, you could implement yourself with Xtras (extensions).
Flash eventually supplanted it on the web due to its lighter, quicker plugin (and content tended to be a lot smaller/quicker to load being heavily vector based) and with CDs no longer being a thing, Director started to lose its way. It pivoted on the web towards 3d, trying to target games, but that never really took off, especially as Flash started to go that route as well. I'm surprised this hasn't happened sooner.