The difference is that if management of the average publicly traded stock shopped it around, they could probably find a buyer for 50% or more of current market cap. Maybe not for the biggest companies like Amazon and Apple. If a substantial fraction of BTC owners tried to exit, they'd have more trouble getting close to nominal value.
For something like this a metric known as enterprise value is used. Assets - cash + debt AKA the takeover price. You can find these numbers on the company's balance sheet. The average company is traded at something like 3.5x their book value (Assets - debt). The market value of a company is likewise some multiple of their EV.
