Using blood may be cheaper, but it's certainly not easier. It would get everywhere, including possibly on the audience. All the kids prom attire would be coated, not to mention the floor. So when Carrie returns home her house would already be covered in blood. It wouldnt work.
I think the projectons were really effective and creative.
Thei production doesn't have a big ass staircase to cover all the blood on the floor.
"The sexual energy between the mother and son really concerns me!"-random woman behind me at Next to Normal
"I want to meet him after and bang him!"-random woman who exposed her breasts at Rock of Ages, referring to James Carpinello