Pega Field Service: Dramatically Decreasing DSO

What new can be said about reducing Days Sales Outstanding (DSO)? It should be a simple matter of invoicing quickly and accurately for work performed or materials delivered. Yet, we typically see oil field service (OFS) company DSO numbers in the 60 to 90+ day range. Why is this?

Today we use our phone to shop, buy, and track orders, so why is the oil field still using paper tickets as a primary means of tracking work performed and materials delivered?