I know nothing about how Cursor is implemented, so this may be wildly off base, but...

Perhaps it is written using some kind of JavaScript framework that doesn't allow access to the process environment by default, but this lets them work around that to access the environment like a native app?

One reason you'd want an IDE to have access to your environment is to enable any tools/compilers/whatever you launch from the IDE to inherit the environment (say, to access SSH_AGENT_SOCK, or whatever).