My first reaction is that this was a short sighted move. The costs for providing the magical express have got to be quite expensive. However, it's a GREAT way for keeping families in the Disney bubble. With the Magical Express, families are locked into making all of their purchases at Disney and I wasn't sure why they would want to give that up.
My guess is that Disney is thinking that with Brightline they will get essentially the same thing and can shift the cost onto the consumer. I would be surprised if they don't figure out a way to make it easier for families coming in on the Brightline to Disney Springs station (i.e. luggage transfer).
As the parent of twin boys in car seats, the ability to leave our car seats at home was a major factor in deciding to go to Disney World next month.
If they don't do something to make it a little bit easier for families (and young families in particular), I think this will end up being a very short sighted move. If I have a rental car, you better believe I'm stocking up on stuff for quick breakfasts and snacks at a nearby grocery store to save potentially hundreds of dollars on snacks and small meals at the parks....maybe I am in the minority though.
The new train service is going to take a while to come online. (There are rumors that delays from their current timetable won't be a surprise.) I don't think that was much of a factor.
Most likely it is this simple:
1) Most people who tended to use DME before will continue to use the replacement services from Mears or ride-shares - but now they will pay their own way into being trapped inside the bubble. It will still be cheaper than renting a car.
2) Some of those former DME people may rent a car to stay onsite, but Disney will collect parking fees from these additional rental cars.
Disney saves money or Disney makes money. The Mouse wins. (Unless people decide that staying onsite is seriously overpriced...but that's not new. We'll see.)
(I am a cheapskate who stays onsite a little with DVC but supplements those stays with more offsite trips. I typically drive so I have rarely used DME. Breakfast groceries and snacks have been in my playbook for a long time...)