There's no security benefit to doing this versus demand-downloading hashed-locked components on need.

Ok, it's probably not a security decision. It's a common pattern with both storage and memory management to push most reservations to initialization, in order to cluster resource insufficiency errors to a specific install-time when the user or admin can do something about it. An excessive just-in-time approach in both storage and memory would cause OOM and Disk exhaustion to occur at many different times.