Having worked as a micro section technician, IPC Certified to 6010, 6011, 6012 and 6013, I've seen a lot of changes to PCB's over the years. During the development of a board some components may be included for testing and calibrating. When a final design is established there are two choices: Modify the schematic or modify the board. To change the schematic you simply need engineers to make the necessary changes to the file and change the revision (up one level - usually) as well as the BOM (Bill Of Materials). But to change the board itself you need to revise all the silk screening and the layers of the board (circuit traces). Solder mask also needs to be changed. All that means a whole new setup for the machinery involved and new lithographic's. From a cost standpoint - it's easier to say DNP on R334 than to completely rebuild the board.
On some "Universal" boards, the way they are configured can mean using the same PCB Layout but installing only certain components while other parts of the board may remain unpopulated. I've seen this with PLENTY of communication boards where a single design board can be configured to work in several different applications. To include DNP on ALL the unpopulated parts would be time consuming and costly. And MANY other boards have spaces for components that were never installed. At one point they may have been a part of the design but with revisions those parts may have been replaced by other component values elsewhere and R334 is no longer needed.
On some "Universal" boards, the way they are configured can mean using the same PCB Layout but installing only certain components while other parts of the board may remain unpopulated. I've seen this with PLENTY of communication boards where a single design board can be configured to work in several different applications. To include DNP on ALL the unpopulated parts would be time consuming and costly. And MANY other boards have spaces for components that were never installed. At one point they may have been a part of the design but with revisions those parts may have been replaced by other component values elsewhere and R334 is no longer needed.