Because different items may offer different grounds for testing. Duh!
You still haven't offered a single cogent reason why 2 curtain rods found in the Paine garage would be tested for Mr Oswald's prints. But I guess 'Don't know, don't care' was your way of giving a 'straightforward' answer!
And you must have missed this part of my response!:
"[to] determine whether they might bear prints belonging to known subversives or possible confederates of Mr Oswald"
Imagine---------for example-----------the prints of Mr J Ruby or Officer J. D. Tippit had been found on the automatic ball-point pen!
Or on One bar pink "Lux" soap or on the plastic box containing tweezers and two pieces of cotton, or on one tube of "Colgate" dental cream, partially empty, or on two large paper clips?
Or on 2 curtain rods found in the Paine garage?
I repeat my question with specific reference to the list of items you have given us:
Were any of these items submitted for fingerprint testing 8 days before being found?
What is the point of your question? It's a rather stupid one.