Actually no, they don't buy code. They buy the people to implement a system at scale, and keep that system running and users trained. The code is negligible.

Take Windows desktop. It's designed to run at scale, out the box, when you have 10 000 employees, and any hardware, printers, whatever. A govt isn't buying Windows its buying active directory, and the fact that every new hire knows how to use it already. And a million other things windows does at scale (technically and humanally).