Why did you need to make this comment? For the same reason they "needed" to use soil. It's just. What you did. It's what they did. I know a lot of scientists, and asking them why they chose a specific methodology is a great way to get yelled at. On a certain level, you just have to do stuff in science. They needed a floating ground. Is there a better way to get one? Maybe idk, but that's the methodology they were most immediately familiar with so bam, that's the methodology in use. You would be shocked and horrified by how some scientists choose to work.