Multiply by count in schedules

When we try to multiply with the Count parameter in Revit, it spits out: "The field Count cannot be used in formulas.

For example, in a furniture schedule, after assigning $ values for various furniture, one cannot get an extended total for a set of particular items using the calculated value (= Count * Cost)

The work around is to create a calculated value named "ExtCost" (= Cost) which is equivalent to the cost parameter. The result looks like this.

Then go to the schedule properties > Formatting tab and select the ExtCost parameter and check Calculate Totals.

The result,

looks fine. But why do I have to do this?