Genuine question:
Why is it that, if I commission someone for an art piece, pay them for their service, must I then still pay another separate fee to use it how I want to?
I always pay my artist what they ask for, but this concept is lost on me.
Meant to be informative/learning

I get the point of different types of commissions, I speak from a consumer's mindset who is lost. I've paid both types but the concept of why it's like this for MY idea after paying for the service is lost on me.