You have a point that there are a lot of separation mechanisms and that, if things were designed better, fewer would be needed but by the same argument it also seems unwise to increase the number of mechanisms to share data. Sockets by themselves are quite big enough on their own to quite literally drive the whole internet through.

A socket is just a raw byte stream. It's a solid base layer, but you'll have to implement your own communication protocol on top, and it'll require copying the data from one process to another. A "stream" is the wrong metaphor for local data sharing.

The data is already in memory and the source program knows its "shape"; there should be an easy mechanism to provide access to that by default, like /proc or gdb but for arbitrary data structures and with better UI.