You are correct that Portfolios are not accessible from within a ticketing application. The reason for this is that portfolios can be used to group up projects, requests, and tickets (even from multiple applications).
Allowing the portfolio to be accessed from a ticketing application could potentially allow users to view items to which they normally would not have access, such as tickets from other platforms.
I hope this helps to explain why we do not support viewing Portfolio information from within a ticketing application. Please let us know if you would like additional clarification or there's anything else we can do for you.