That’s nothing new. There have always been mail-order retail office suppliers like Quill to compete with. Office supplies are one of the best-suited product lines to remote sales, because you never need to inspect a ream of paper to make sure it’s the kind you need. You just say “gimme 5,000 sheets of white letter-sized paper and 500 black ballpoint pens” and so on.
Quill has been a subsidiary of Staples since 1998. And at my office, we get supplies from Staples, delivered by a guy who wanders around the building delivering whatever was previously ordered by each department. I don’t know if this is actually from the Quill division of Staples, or another one.
Sam’s Club predates Office Depot, et al by a few years (1983 vs. 1986), so in a sense, they’ve always been in competition, except those first 3 years.
I suspect that most cities always had their own wholesale office supply companies who supplied most of the staples, paperclips, pencils, manila folders, etc… and the warehouse stores and big-box office stores probably killed them off due to economies of scale and correspondingly lower prices.
I have a feeling that online ordering from the existing outfits as well as the new ones like Amazon have changed the playing field and left stores like Staples out in the cold somewhat.