What you also seem to be forgetting is that piracy is illegal.
It is. But they fail to understand that if they want us to buy their games they have to convince us it is worth it. And how do we suppose to know it?
Do they fail to understand that by streaming one DOES NOT illegally distributing the game - it is only sharing a personal experience. And - if there are no footages of the game (except for those on developer`s site) - maybe it is not worth playing.