When I hover the mouse above the issue type icon, it shows change issue type.

However when I select it, I can only see the same issue type as an option.

All issues in this project are on the same workflow, and the issue type field is configured to show on this page.
Why is the only option to change to the same issue type? What else am I missing to convert this?
I know that I can just use the 'Move' function, but I'd like to know how to configure the other way, which I've seen in jira's own KB is a possibility.
TIA