For one thing, the DPO metric is the counterpart of the Days Sales Outstanding metric, dealing only with sales of goods. Another thing is that if you try to include ALL payables and their expenses, then the CAPEX items affect you. What would the metric look like if you include purchase of a large machine costing 1,000,000 Lira payable in a year? The large amount in A/P will affect your metrics. Also, how to deal with depreciation expense? So, the DPO metric has a defined narrow method of calculation to keep it effective.