I don't believe dorsiflexed preloading is real. Sprinters dorsiflex in the air but always plantar flex well before footstrike, re-shortening the calf muscles which are then re-lengthened during the footstrike before snapping back and re-shortening. If anything preloads them for that it should be the plantar flexion.
I think the real reasons it works, which it does work, is to shorten the lever arm of the lower leg allowing for higher cadence, and to allow the upper gastrocnemius to contribute to flexion at the knee.
The gastro is biarticulate, crossing both knee and ankle. Muscles apply more force when longer, so when biarticulate muscles flex at one joint, they typically extend at the other joint to compensate and maintain power.
When the recovering leg swings forward and extends before striking the ground, that lengthens the upper gastrocnemius, freeing up the lower part to contract again. Likewise with the hamstrings, which simultaneously extend at the knee and contract at the hip, while the rectus femoris extends at the hip and contracts at the knee. Overall these muscles kind of oscillate like a wave in a slinky.