Marty returns to 1985 to (Lone Pine Mall) because he changed the past just in time to see himself travel back to 1955, if he had stopped this version it would have caused a paradox because they're the same person but how and why Marty is surprised by the changes to his house and family, he'd already know! Doc's video would also say "I'm standing here in the parking lot at Lone Pine Mall"! 😏