Just because it's portable doesn't necessarily mean that it's allowed on the organizations allow list, but it does seem highly unlikely that the organization doesn't have any alternative text editors allowed.
But maybe they don't edit text files often enough to bother. And honestly, notepad was recently updated with tabs which makes it a lot more usable that it used to be.
They look identical in most fonts, which is a huge problem for my open source project to simulate the former Vice President. It's called: OpenAl.