"What's the benefit of this?"
User engagement. That translates into money.
Now I can see it can make for a fun party game, but that they seriously go after it, when their game should be leading models to do serious work ... is not a great sign to me.
And users paying to generate longer videos.
Not only it has the slot-machine like addiction factor, it's going to make lots of money and it will take off very quickly.
All OpenAI has to do is to make the video generation much much faster.
It will only take off, if people like it, if it becomes trendy and this will strongly depend on the quality of the generated videos.