Why aren't preference shares included in market cap calculations?

Preferred shares are not included in your standard market cap calculation because their characteristics are more like debt, thus equity value to common shareholders is reduced by amounts owed to preferred shareholders. With publicly traded companies, preferred shareholders are essentially debtholders entitled to a periodic (generally annual) interest payment equal to the par value of the preferred shares multiplied by a pre-stated "preferred dividend" percentage, determined at issuance. For instance, if I hold Series A Preferred shares in XYZ Company and I bought them at $100 per share with an 8% cumulative annual dividend, I am entitled to $8 from the company every year. Very similar to an 8% annual coupon rate (interest) on bonds with a face value of $100...