Uzmati, the rumor about why Monorail Orange got scrapped is kind of funny. The rumor goes that a veteran monorail pilot was retiring/being fired, and he wanted to go out with a bang. Suppsoedly on his last trip, he told all of his pasengers this and told them to hold on for "[CM's name, I don't know what it was]'s Wild Ride!" And he took off at full speed, and never slowed down, even during all the curvy bits over Tomorrowland, except for a screeching halt at the station. Rumor goes that this joyride mortally wounded Monorail Orange, and it was taken out of service. Later, it was decided it would be cheaper to scrap it opposed to fixing it.
That's the rumor as to why Monorail Orange had to be taken out of service. How much of that is true or not is up to debate. I haven't seen any evidence to prove or disprove this.