Fiochis come in boxes of 10 and I have gotten cheap federal slugs in boxes of 15. Can you imagine what a box of 25 remington accutips would cost? It would be almost $100 after sales tax.
I think originally they came in boxes of 5 back before the way overpriced slugs came out because they were never viewed as something you would go out to the range and shoot for accuracy. Back in the olden days, they were considered close range and were shot out of smooth bore shotguns with bead sights. That would be my guess, at least.