It might help to check your fare rules, especially for the original ticket. I suspect that DL agents have given you special favors in rebooking you from domestic FC to D1. When I look for domestic FC flights, often the fare rules specify that certain flights/routes/aircraft cannot be used and the prohibitions seem designed to apply to D1 flights. Alternatively, I see fares that include D1 segments priced significantly higher for the same city pairs.

ADDED: Do any of your ticket receipts indicate a broken fare? Also, what are the current legal routings for YYZ to PSP as your rebooked tickets seem to be taking the long away around to PSP from Canada.