What actually makes them amateur at this point? Wouldn’t it behiove them to incorporate as a non profit perhaps?
That they're hobbyists doing this in their free time? It says:
> We’re an association of 50-60 unpaid, volunteering members and we build our rockets in a workshop in Copenhagen, Denmark. That requires many different skills, so we’re a very diverse group, from blacksmiths to rocket scientist. We all do this in our spare time, working regular day jobs on the side.