That is normal behaviour, if you start a new PS session, you have a new environment.
All the variables you have in a specific PS session, are unique to that session. They are not copied to a new session you start from within the first session.
You can start new sessions from within a PS session by executing the powershell.exe command or by executing the Start-Job cmdlet.
And you could use for example environment variables to pass information between the scripts.