Disclamer: i can post artworks keeping commissioner anonymous - no nickname mentioned , no tags when i will be posting it on social media - this would be free of charge.
Private commission means: I don't have right to show it to anyone ever.

So why is extra fee for private commission?

1)

i won't ever be able to use this art work anywhere to gain value such as: more potential commissioners or show it as example for commissioners (if current artwork is related to their commission idea)

Example: potential commissioer wanted to see how i animate transformation animation for profile picture...i did have one in my possession but i had no right to share with it, so i spent few hours to draw an example for customer...and well they never came back to me so i just wasted my time. (which i could spend more efficiently)


2)

it means i will deliver less monthly content for my patrons if i will be working mostly on private art


3)

i can't stream private art which leaves me again spend less time gathering audience



4)

i also basically partially surrender my rights on the art piece since i loose the all abilities to passively benefit from it (use for advertise/portfolio/print it for conventions)