Why does rendering cost so much?

Could you explain why rendering costs so much? I've been puzzled about this for quite some time. I understand that rendering involves complex calculations and the generation of realistic images, but I'm still not quite sure why it commands such a high price tag. Is it due to the powerful hardware required? Or is it the expertise and time investment needed by the professionals? I'm keen to understand the economics behind this process and how it fits into the larger picture of the filmmaking industry. Could you please break it down for me?