It's not necessarily bad if you have someone amazing in charge of casting, but it's really hard to build a cast out of people who nobody has heard of who it tur

It's not necessarily bad if you have someone amazing in charge of casting, but it's really hard to build a cast out of people who nobody has heard of who it turns out are actually incredible talents. Known actors are a known quantity in that regard, which is why it's safer to go for them. Normally you'd expect there to be some on a big budget project that isn't taking risks around quality.