Here's the official pitch from Disney:
https://disneyworld.disney.go.com/guest-services/magical-express/
The top of the page features this pitch:
Disney's Magical Express
Start and end your stay with complimentary motorcoach transportation for you and your luggage to and from select Walt Disney World Resort hotels.
Yes, is says, "complimentary motorcoach transportation for you and your luggage."
The page goes on to say this about the DME luggage service:
Be Magically Whisked Away
Board a motorcoach at Orlando International Airport and well get you and your bags to your Disney Resort hotel.
When you reserve Disneys Magical Express, you can begin your vacation the moment you step off the plane. Bypass baggage claim and avoid the inconvenience and cost of driving or finding ground transportation. With this special benefit of staying at select Disney Resort hotels, get from the airport to your accommodations in comfort and have your bags delivered directly to your room. Youll also enjoy a complimentary ride back to Orlando International Airport on the day you check out of your Disney Resort hotel. Please note that pets are not permitted on Disneys Magical Express but service animals are.
Luggage Delivery Service
This feature of Disneys Magical Express is available for flights arriving between 5:00 AM and 10:00 PM daily. Your luggage will travel separately, and it may take up to 3 hours after you arrive at your Disney Resort hotel for your luggage to be delivered to your room. Please pack any valuables, medications or anything you need immediately upon your arrival in Orlando in a carry-on bagand have your MagicBand with you and easily accessible at the airport and when you arrive at your Disney Resort hotel. You do not need to be in your room to receive your luggage.
If your flight arrives before 5:00 AM or after 10:00 PM, please collect your luggage at baggage claim to bring with you on the motorcoach. Please note: Disneys Magical Express service does not provide luggage-only transfer. You must be present on the motorcoach to have your luggage transported to a Disney Resort hotel.
The key line is, "You do not need to be in your room to receive your luggage."
Essentially, Disney is saying your bags will be in your room as a benefit of staying at a Disney resort and using Disney's complimentary end-to-end transportation and luggage service.
Disney's pitch does not say anything about tipping, one way or the other.
I'm well aware that "complimentary" does not equate to "no tipping." For example, if a restaurant has complimentary valet parking, it's still customary to tip when the car is returned to you. In that case, you have personal service and direct interaction with the person returning the car to you.
However, the way DME is structured and presented, with guests typically never seeing the person who delivers their bags, it is not surprising that most guests do not tip for luggage delivery and do not consider that tipping is even possible.