That's mostly a function of the studios drastically reducing the amount of time given to produce the work, while simultaneously increasing the complexity.

It's fair to say that not all vfx facilities produce the same quality of work. That's a function of many things, but primarily if the facility can charge a higher rate they can afford to employ more experienced staff and put more of them on a project. Same with any business.

However not everyone wants to pay what ILM or Weta are charging.