There are likely a number of reasons which led to this.
Partly it's because they want to give you the choice. They don't know if you want a 3 foot or a 16 foot; if you want a regular one, a gold-plated one, or a retractable one; or maybe you want to use the printer with parallel or ethenet; or if you already have one and don't want to pay for another one.
(Realistically though, they really could just toss a regular 6-footer in, since that's what everyone buys.)
It also may be to keep costs lower on the printers - although these cables cost less than a dollar or two to make, so that's not much of a reason.
The most likely reason is that it gives the retailers the opportunity to make some money. Stores don't make a lot on many products. Printers are probably 10-30% profit, they will often lose money on a laptop, but cables and other accessories are where the big money is. If they're selling a usb cable for $20-$30 that cost them $2 or $3 to buy (and less than a dollar to manufacture), then that's probably going to be well over 90% profit for them. That may be surprising to some, but it's very real.
What?s the deal with not getting a cable with a printer? This topic came up briefly at the end of the 9/5/ podcast.
I?ve always marveled at how the shelves at Best Buy are filled with $25 USB cables. I?ve never found an explanation as to why the cables are so expensive. I assumed that printer manufacturers stopped including them to keep their unit price down.
Then I purchased a no-name hard drive enclosure from an online retailer. I was very surprised to discover when I opened the box that this device, which cost $35, included both a firewire and a USB cable!
Is the mob controlling the distribution of packaged USB cables? $25 is just too damn much for 6 feet of wire and a couple of connectors. Can someone shed some light on this?