Publicly, Disney was all-in. But this always struck me as a commitment borne out of supporting the community. As in "you want to bring more mass transit to the area? Yeah sure, we'll help."Nah this is 100% about Universal getting a stop. Disney was all in until then.
Whether Disney was driving the plan 2 years ago or the SR-417 route was the plan presented to them, it made some sense (to Disney) at the time. Now with Universal included, it makes less sense. With more people staying at resorts in the WDW area than Universal, US has much more to gain from a DIS+US rail connection than DIS does.
That combined with the logistical hurdles of moving people from two dozen hotels to this rail system may have been the tipping point. Universal's property is expanding, but still much more compact than WDW with their proposed station right next to Epic Universe. At WDW, the station isn't walkable to any destination and you're bussing people as much as 7-8 miles away to MK and AK area parks & hotels.
Yes withdrawing makes Disney look petulant. But I think practicality played a larger role. I just don't see this catching-on as a form of airport transport.