Why in India people eat sitting on the floor?
“This tradition is not just about sitting on floor and eating, it is regarding sitting in the ‘Sukhasan’ position and then eating. Sukhasan is the position we normally use for Yoga asanas (i.e. yoga positions). When you sit on the floor, you usually sit cross legged – In sukhasana or a half padmasana (half lotus), which are poses that instantly bring a sense of calm and help in digestion, it is believed to automatically trigger the signals to your brain to prepare the stomach for digestion.”
NB: It was brought to my attention that the above message answers the question of the lotus position but not the eating-on-the-ground. In my opinion, 1. It is easier to sit in the lotus position on the ground than on a chair, 2. Indians usually living numerous in a small place, it is more practical not to have a table (it takes less space and anyways when you eat with your fingers you don't really need a table: you can hold your plate with one hand and bring it to mouth level (if required) and use the other hand to grab food), 3. You feel less hot on the floor. It is just my opinion though...
Source: 20 Amazing Scientific Reasons Behind Hindu Tradition: http://desinema.com/hindu-traditions-scientific-reasons/