Well it's a mistake that they are going. Inexpensive and familiar, it was a place for a quick snack or a lesser priced meal. I didn't care if McDonald's was in the parks, but it always provided another option.
As for why? Here is my take. I am a 30 year veteran of fast food. Restaurant economics are much tougher these days, and you cannot make money in locations with high rent. You just don't make enough per sandwich to cover your costs. I bet that their agreement was up for the location and they elected to leave due to Disney asking for a big raise in rent. They are betting that the location over by the AK will benefit due to being the only McDonalds on property. It wasn't a coincidence that they remodeled it just before this one closed. So at the end of the day I am betting that the DTD location simply could no longer turn a profit believe it or not. They are betting that the location by AK will.
That's also why no other fast food competitors (i.e Wendy's, KFC, BK) have shown up. Pollo Compero can charge a ton more for it's food and make a buck. Also, the company is trying very hard to expand their base in the USA and they may be willing to break even (maybe) to get the exposure.
Even though McDonalds can charge more on Disney property than a regular location, they can't jack it up to the point where people walk.
So we are losing one of the few locations in DTD that you can eat at fairly cheaply because they couldn't charge enough for their food.
Disney should have done what it could to keep them.
Typical fast food agreements are for 10 or 20 years. You can bet that the AK location will be around for quite a while.