RunDisney has tried a number of ways to convey running etiquette over the years. When I started with RunDisney, they talked about running etiquette in the pre-race spiel. They've had sections on etiquette in the old printed race weekend guides and subsequently in the electronic guides. For the last few races they've tried putting etiquette postings out on social media. Unfortunately, few, if any, paid any attention regardless of the medium and the same problems recur race after race.
At some point, the runners have to take some responsibility for the situation. At this point, I don't know what more RunDisney could really do beyond making runners take an online course and quiz prior to being allowed to pick up their bib and hoo boy, it doesn't take any imagination to see how that would go over!