A prequel is an automatic retcon. There will always be questions like "why didn't they have that thing in the stories that take place afterwards?"
Besides, backstories are meant to be imagined by the audience. As soon as you decide to make a prequel you're choosing to create cognitive dissonance for the fans. When people have to choose the backstory they imagined vs. the backstory somoene else came up with and put on the screen, people are going to choose the backstory they imagined.
Prequels are always bad for the fans, but the studios like them because it's a lower barrier to entry for the non-fans.
Yeah it's the old "No True Scotsman" fallacy.