They don't need to convince their already huge and already convinced core users, so there's not much point in building big tech demos that apply in that space. The aspirational AAA stuff that Unity puts out does 3 things I think:
- convince current indies with big dreams that their investment in unity has long legs if they grow larger and more ambitious.
- open up to non-gaming gfx tech sectors: broadcast, movies, simulation, etc.
- push their engine to its limits so they know where it hurts the most in places that actual users are not pushing. (it has many known rough edges and areas, but Unity users already report these)