That's not entirely true.
You'd need to qualify it with, "The way WDW is currently designed, there's no way..." They may not be able to 100% prevent alligator presence no matter what, but they sure as heck didn't have to make an ideal habitat for them and invite them on in to mingle in guest areas, either.
Basically, we are seeing the long-term impact of what they did 40-50 years ago when they flooded that swamp to make a vacation paradise. The design flaws of the open water-ways, essentially creating an incubator of predatory animals who after several generations have become very accustomed to humans and have become unnaturally close to them. They really couldn't have done it any "better" for the effect to have happened - a populated yet somewhat isolated area with in and out access.
As pretty as the beaches at the GF and the Poly are, they were TERRIBLE ideas. They didn't take into account the ecological changes that would occur. Today, they wouldn't have been allowed to do it, period - flooding hundreds of acres for a non-functional, cosmetic reason (they wanted to make the illusion of "waterfront" property). I'm far from a tree-hugger, but even I can see the folly in the venture.
I expect long-term, WDW is planning wholesale changes to the entire area.
As to the report, aside from of course the sympathy for the actual victims, I also feel badly for the CM's involved. I have no doubt whatever they did or did not do with the guest complaints was per Disney policy - one imagines they got sightings nearly every day that amounted to nothing even when dutifully reported. The larger institutional issues here aren't their fault, though I am sure they will forever feel some form of "If only I had..." guilt that they didn't earn.