how would any alternative design prevent intended behavior?

But the most obvious alternative to a filesystem would be formatting a whole hard drive as an sqlite database. Obviously it would be a radical rethink in OS design.

There are also "single-level stores" from the last millennium - designs where there is no separation between volatile and nonvolatile storage. All memory in these systems is treated as nonvolatile. A Word document, for example, would be something like a suspended Word process. A directory is a process that only manages pointers to other files and directories. Obviously processes must be extremely lightweight in such a system. KeyKOS is an example of this and you can read papers about it and its Unix emulation layer. This is one of the many things humanity explored before settling on the hierarchical filesystem as the base layer of storage.

> But the most obvious alternative to a filesystem would be formatting a whole hard drive as an sqlite database.

At the end of the day, you'll be chasing pointers inside that SQLite database, where you store tables, indexes and such. Interestingly, this is how a filesystem works. Tables, indexes, redirections and fields. Very much like a database. EXT4 is a table of redirections, nothing fancy [0].

[0]: https://blogs.oracle.com/linux/understanding-ext4-disk-layou...