its not about moral grounds. its about class struggle and the bare minimum for a union is defending hard won gains for the working class. your example with the truckers doesn't translate because no union truckers (that I know of) have had such a battle won that would guarantee residuals on what is being transported. what is not a winnable battle in one sector is a winnable battle in another. the question really is which side of the fight are you on?

if you are a small business owner you are not in the same position as a worker that is part of a union that has a negotiated contract, so I can see how you think you have no leg to stand on when asking for residuals but what it ultimately comes down to is always leverage and with collective action workers have more leverage than you would on the open market as a freelancer, for example

that said, though, there are attempts at unionizing platform freelance workers such as people that work through platforms such as fiver or upwork, etc. i haven't kept up on how well they are going but you could reach out to union organizers where you are located to talk to them about that