Why stock market defies the natural law of economics?

In Economics, its stated that with higher prices, demand falls and when prices drops, demand increases. Its just the opposite when it comes to stock markets. People buy when prices are sky-rocket high and they stay away from stock markets when its cheap. People often turn a blind eye to stocks when the valuations are at dirt cheap and will rush to grab when the valuations are sheer nonsense. Its very difficult to comprehend this situation when people don't buy a dozen of banana at high prices, then why they happen to buy stocks at costly valuations. When people stop buying and consuming a kg of onion at Rs. 40-50 as part of their food, then how they were able to buy Suzlon Energy at Rs. 500, Educomp Solutions at Rs. 800 or DLF at Rs. 1200 prior to the recession of 2008-09. Currently, Suzlon Energy is trading at Rs. 15, Educomp Solutions at Rs. 158 and DLF at Rs. 205. And when people rush to buy a kg. of onion at Rs. 20-25, they were too sceptical to buy Hawkins Cookers at Rs. 130, TTK Prestige at Rs. 90 or Titan Industries at Rs. 35 during the downturn of 2008-09. Currently, Hawkins Cookers is trading at Rs. 1800, TTK Prestige at Rs. 3100 and Titan Industries at Rs. 275. This is where investors defy the basic law of Economics that with higher prices, demand falls and when prices drops, demand increases. People are all vice versa to that in respect to their stock investments. This is a question worth pondering over. I'm not able to find the answers. Perhaps people can. Kindly comment.