NFA tax stamp - why is it called a tax stamp when there is no tax on it?

I get it - the NFA was a tax stamp in the 30’s and 40’s. But today it isn’t; it’s a fee. Why hasn’t the name changed? It’s still called a tax stamp, a tax on NFA items. I can’t seem to find a reason as to why it’s still called that. It’s like a tax stamp on some of our rights that we have.