Lots of people implement half of TCP over UDP because they want packet based transmission but also care about losing packets.

Implementing packets on top of a stream is not as trivial as implementing a stream over packets.

Implementing streaming files over record-based files is easier, you just iterate over each record and append to the stream. Implementing records in stream-based files means you have to define a framing format, internal format, bookkeeping, etc.

Record-based files would be the proper lego building blocks.

The idea behind the author's post is that a directed acyclic graph is a basic block that is just one layer of abstraction above raw bytes. JSON, YAML, TOML, INI, .properties, environment variables are all just different ways to represent a graph and if it were possible to store the graph directly in the filesystem then one would not have to manually [0] serialize the graph to bytes and deserialize it back later.

[0] graph -> byte conversion is the job of the graph filesystem

Sure. And we have, many times over. A base implementation that supported fixed and variable records, shared process mmap() access, etc...would have value. And perhaps the kernel being aware of it would have some benefit.

And the normal programmer's logic is: "if it's not already integrated in the OS then I am not going to use it". So stream files it is, forever.

I think history has proven this. People are very risk-averse even if the risk is quite minor (example: using sqlite3 instead of the file system).