The difference in this case is that the stock market is a highly efficient process, where feedback paths are short, information is shared widely, and there is potential to make a lot of money on other's misjudgements, automatically correcting the price in the process. This means changes in confidence are almost immediately reflected in the price.

T-shirts, on the other hand, much more slowly change to match confidence, for the same reasons. If you think people collectively over- or undervalue T-shirts, it is rather hard to make money off of that mistake. In part because it implies moving physical stock, but also because they are a relatively refined product. Markets for natural resources see some of the same fluctuations as stock markets, although not to the same degree.