The difference here is that a running shell (including the shell environments that services run with in) are an abstraction layer about managing processes. Within that abstraction layer, each process can have its own unique environment variables that they can change and manipulate independently. That makes them not global.

Within a process the top level abstraction is the process itself, and anything underneath (class, method, function) will be impacted if another sub-abstraction makes a change to a global variable.