According to the source, McDonald's has been waiting for the 10-year exclusive movie tie-in contract with Disney to expire for years. Apparently the company felt that the original deal with Disney was too one-sided and was never going to renew it.
The exclusive contract with Disney did not allow McDonald's to tie in with other blockbuster movies such as Star Wars and Shrek thus leaving such titles to their competitors - even when the films would prefer to tie in with McDonald's (McD's market share is larger than all of its competitors combined). Deals are about money and rarely anything else. The decision by Disney not to renew exclusively with McDonald's likely came down to dollars and cents.
Disney's decision not to renew its marketing pact with McDonald's doesn't prevent them from marketing their films through the fast food chain however. It's expected that Disney/Pixar will still be tying in with McDonald's for promotions on certain films, but it will only be on a title-by-title basis. What's gone is the exclusive relationship. Also, because the exclusive relationship is gone Disney/Pixar is free to promote their films with Burger King, Wendy's or Taco Bell. So don't be surprised if you see their small plastic figurines again in a drive through near you.
So much for caring about childhood obesity, I guess.