[Edit- I may have misunderstood your question, but I'll leave my reply anyway.]
Here are some possible reasons you might use Bink instead of a free codec:
- Bink video has been around for a long time as a product, even though the codec has been updated (probably multiple times, I don't know). There weren't always good-enough free codecs, and if you have prior experience integrating Bink with your stuff then you may prefer to stick to something you know is good even if it costs money.
- RAD focuses on producing libraries that are very easy to drop in, specifically in the context of games. They know how game code is written and structured. They know game developers want to be able to integrate video in a way that works -- and performs reliably -- within an existing game engine that does a lot of custom management of textures/buffers/graphics memory. State of the art free codecs don't necessarily have free libraries that are actually high performance and easy to integrate within a game context.
- Your state of the art free codec might work great on a modern smartphone or PC, but good luck getting it to work on a Nintendo Switch or whatever weird console you're targeting. Bink is available for whatever game-specific platform hardware you're targeting.