I don't think I've ever seen a schematic for a program in all my years programming. Now that you mention it, it really is peculiar given most if not all other schools of engineering have schematics drawn up at some point or another.
To be fair, all other schools of engineering concern themselves with constructing actual physical objects, not abstract intangible mathematical structures.
To be fair, our school of engineering has moved from parsing payroll and accounts payable and is now controlling physical objects and their interactions with the physical world, so, its probably time to start taking things seriously like our peers
That doesn't make the programmed parts any less abstract, though. That the system as a whole contains physical parts just makes it easier to schematize the system as a whole, not necessarily each individual part by itself.
I'm not saying what should be done entirety other than pointing out its become a serious discipline with real world consequences but lots of it is still treated as bofh doing perl in the basement with no checks or oversight or standard process.
I suspect they aren’t used often because most programming is carpentry rather than engineering. Which isn’t intended as a slight… my life would be much less pleasant without furniture.