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.
Thinking something is over or under valued is very different from general confidence in the economy. In daily life you're not betting on the economy, you're part of it. You work and spend even if you think the nukes are going to kill everyone. Confidence has a vastly weaker connection to demand for goods.
If people think the dollar is significantly overvalued, they'll switch to gold, bitcoin, rolls of toilet paper, or other forms of ad-hoc currency. That's what happens in countries with 1000% inflation, for example.
