My theory on seed steeping: we're just adding an additional solution so diffusion is happening in multiple directions. We're making our juice multi-task.
Diffusion simply is the movement of molecules from an area of higher concentration to an area of lower concentration. When you have, say, 27ml fluid of 0% flavor (your base) and 3ml fluid of 50% flavor (number is pulled from my rear, but used because flavoring isn't 100% pure flavor particles), there's a fair amount of diffusion that has to take place. It happens in one direction: flavoring diffuses into the base. We shake and heat to increase molecular motion in order to speed that diffusion up.
Seed steeping changes 27ml of 0%, 3ml 50% flavor to something like 24ml 27ml 0% base, 3ml 10% pre-steeped, and 3ml 50% flavoring. Instead of diffusion happening in one direction, it's happening in THREE directions. Flavoring is diffusing into the pre-steeped juice AND the unflavored base, and the pre-steeped juice is also diffusing into the unflavored base. More diffusion = more rapid homeostasis.