Comment by andrewstuart

I don't think this is the real explanation. If they gave the filesystem a list of files to fetch in parallel (async file IO), the concept of "seek time" would become almost meaningless. This optimization will make fetching from both HDDs and SSDs faster. They would be going out of their way to make their product worse for no reason.

Which is true. It’s an old technique going back to CD games consoles, to avoid seeks.