When a company's stock price decreases, the market capitalization of that company also decreases. This is because market capitalization is calculated by multiplying the current stock price by the number of shares outstanding. So, if a company's stock price decreases but the number of shares outstanding remains the same, the market cap will also decrease. There are a number of reasons why a company's stock price might decrease, including poor financial results, negative news, or simply a general decline in the stock market. When a company's market cap declines, it may be seen as less valuable by investors and its stock may become less attractive to potential buyers.