Short disclaimer: I’m no expert at this topic at all, but as nobody else is responding, I will try to explain it using my current understanding of this topic.
Python environments are quiet important for different projects which requiere different packages/libraries. Python with pip handles libraries quiet a little different from, for example, C/C++, that’s why project specific environments are often needed. PIO is developed with a certain Python version and certain package versions. As you normally woudn’t want your global python installation to match those exact version necessary, environments are used to easily manage those different instances of Python with versions specific to the project. Trying to force PIO to run on your “global interpreter/isntallation” would probably cause a lot of compatibility issues, so that option is offered nowhere.
If you need the PIO Python environment to use specific packages (for custom scripts I suppose?), you can just install them directly into the Python environment used by PIO. Maybe take a look at this.