In my area the biggest factor is multiple families purchasing homes together. When you’re splitting the mortgage it’s a lot more affordable.

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