system
Given the following post, respond as if you're commenting on Reddit:
human
[BTTF] What did Doc and Marty do that screwed up utopian 2015?

There's a retcon theory that the reason *our* 2015 doesn't resemble the movie's 2015 is because Doc and Marty did something in the past that altered everyone's timeline.

My personal theory is that somewhere along the line they got in the way of the guy that invented hover technology. That guy didn't invent flying cars or even the hoverboards, which I assume operate on the same concept. Possibly the same technology that allows one to negate gravity could also be the tech that led to Mr Fusion. 

Any thoughts?
gpt
Hover tech was everywhere in Hill Valley because that's where the inventor was born. The entire place was essentially a cutting edge early adopter of the tech, and essentially served as a living, breathing showcase of what it was capable of...

Or would have been, if the inventor's ancestors hadn't been scared off of setting in Hill Valley by word of rampaging outlaws and runaway trains. Settling instead in the Seattle region, the inventor was born, but didn't make the same connections and friendships that led to them building hover tech. Without the gravity manipulation tech that underpins hover, no one cracks the secret of portable fusion. Without portable fusion, clean energy isn't abundant, leading to a general damping of technological progress.