A few months ago the KRL722 went on sale for $2999, and I think you could get another discount if you financed it through Snap-on Credit.

A few months ago the KRL722 went on sale for $2999, and I think you could get another discount if you financed it through Snap-on Credit.
Thats about 1/2 of list price. Why do people want so much for used boxes then?
Boxes get financed through Snap-on credit, normal tools get financed by the individual dealers. Sometimes they offer financing incentives, just like car manufacturers.
I picked up a Snapon 722 about 2 months ago. No stainless top, still in the shipping crate, brand new. Sat in a kids garage for 2 years untouched. I paid $2200. I did overpay a bit but it was the exact color i wanted and i was able to pay the kid in 4 installments over 4 months.

If you finance a $5k box through Snap-On credit (not your dealer) you pay interest, just like if you go buy a new Mustang and finance through Ford motor credit you pay interest. Late in the year if Mustang sales are stale Ford motor credit may offer an incentive of 0% interest for 24 months on Mustangs. Likewise Snap-On may run incentives of 0% interest, but this I do not know, but they certainly would not pay you to finance the box with them.
"...I know you can get a discount if you pay cash, but why would they give you MORE discount if you financed it??…"
Because they know that they'll get it all back, plus more. It's no secret that it's much better to be a lender than a borrower.