Otherwise, people would just sell open work with little or no modifications.
Nobody want's to buy if the speed isn't improved.
When you optimize you often you need to try 10 different approaches to gain speed, so a few lines of code can take 100hours to make. because the 9 first attempts didn't work.
It wasn't directed to you: you know how much you worked on the code, I don't need to teach you anything.
Still, the license is the license.