That's not really accurate. I can write a small program that does not include the OS, but rather assumes it. Just as a vehicle designer doesn't have to include the gas or electric distribution infrastructure in their design, they can assume it.
If I'm conforming to someone else's interface (say the C standard library), that's equivalent to an electrical engineer assuming various standard interfaces for the equipment they're designing. It's a design consideration, but not a design task. So the project itself may still remain quite small.
When I'm designing the interfaces that others are using, or designing the interfaces between 100 [0] smaller programs so they can interact effectively with each other and their environment, then it's a larger engineering task.
[0] Arbitrary number.
Re:Is Software Engineering Possible?
by paulddraper on Sunday June 11, 2017 @11:19AM
(#14532256)
And likewise, the OS relies on the ISA, not having to know about chip design.
Now - you could go down to machine code, or work on embedded systems, etc etc - but the point remains. It's not just the software you are writing that's part your program, it's also all the other, existing software (and physical designs) it makes use of, or interacts with.
Edit: Might be called "software systems engineering", or maybe "dev ops"?