Even then, if Coca-Cola goes out of business, and the stock is delisted (so the price is effectively zero or close to it), you still own 1 millionth or whatever

Even then, if Coca-Cola goes out of business, and the stock is delisted (so the price is effectively zero or close to it), you still own 1 millionth or whatever of the company, and the company has actual tangible and intangible assets (including its name, which in Coca-Cola’s case would be one of its most valuable) that can be liquidated to recoup value to the owners. If Bitcoin goes to zero, there’s no backing store of value to sell — you own a number whose entire value in other monetary units is based on people wanting to buy it, not on any asset or guarantee backing it.