Companies invest money to create products. Some turn into a profit, some don't, some don't even make it to the market. At the end of the year they sum revenues

Companies invest money to create products. Some turn into a profit, some don't, some don't even make it to the market. At the end of the year they sum revenues and expenses and either a profit or a loss. If a movie makes zero money it's only an expense and that already reduces the taxes on the revenues. SO why do studios have that tax write-off on top of normal tax on the revenues - expenses figure?