Thank you for all of your support, and many apologies for any disappointment or confusion!
Alfred music chooses to sell all their two piano scores as single volumes — two scores are necessary for performance. Publishers choose to deal with this issue differently, but we can see how Alfred came to this decision, and we have chosen to do the same with our own scores published via Awkward Fermata Press. On a logistical level, it can be messy for the publisher to produce a second, differently formatted score and stuff it inside the first copy — this increases the price disproportionately. On a personal level, Liz and I often purchase our scores separately as we practice and live in different cities, so we'd rather not buy two sets and have additional scores left over.
Thankfully, Alfred's prices are extremely reasonable compared to other two piano scores by different publishers, even those not sold in sets!