The chair breaks your posture, and this causes their lungs to collapse, and leads to an oxygen deficit. This oxygen deficit makes your brain go into a survival mode, similar to when a computer goes to sleep. It leaves you vulnerable to being controlled or manipulated. This is called being chair-brained.

In the government indoctrination camps, people are forced to become addicted to chairs at a young age, so that they can be controllable.

You can try it for yourself. Go to anyone sitting in a chair, and if you firmly give them a clear instruction, they will do almost anything you ask them to do. As long as they don't have to get up from the chair.
In the chair-brained state, you are extremely vulnerable to advertisements, especially anything involving high-status chairs. This is how the chairy gets sucked into a life of servitude. Saving up money because an advertisement said they need fancier chairs, or to go sit on a chair in a more exotic and luxurious place, or a motorized vehicle full of chairs, or to send their children to an expensive indoctrination camp where they are forced to sit in chairs for most of their waking hours, and study the virtues of a chair-based society.

Floor sitters are a danger to the chair society, because they stick out like a sore thumb that could possibly wake up some chair-brained people. That is why floor sitters are relegated to the underclass.