Not sure how old the program was OP watched but they found one void in 2017 using cosmic rays. I’m guessing the pyramids are way too solid for ultrasound or x-ray to work.
https://www.science.org/content/article/cosmic-rays-reveal-unknown-void-great-pyramid-giza
In my area the biggest factor is multiple families purchasing homes together. When you’re splitting the mortgage it’s a lot more affordable.