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Most stocks are shares in a company that already have operational founds, and it's really about the valuation of the firm as it is. A high stock-price will help a firm to get good lending deals etc. but they don't use the stock market as a "cash pool".
Right, the funds are not necessarily directly available. But they are are often needed to operate and provide higher valuations to secure loans. But at some point if the value falls to much the company may hit a cash crunch and not have the collateral to take on new debt. If they crash the stock will be worthless. Bitcoin could loose popularity and become less valuable, but it is not going to go broke and could always bounce back.