It's all about ratings.
But it will dilute the votes, making the outcome less predictable, and the offsite gambling more exciting. Again, it's all about ratings.
Brilliant, actually. Because at the end, it doesn't really matter. The same group of elites are going to vote and they will continue to vote based on certain criteria (they're not going to vote for, say, Transformers). But the more popular films they include, the more people will tune in rooting for their favorite films (and pissed of when they don't win). It's also good for the studios to boast that they, too, have an Oscar Best Picture nominee.
What I'd like to see is for them to allow animated features to be nominated for best picture, instead of their own little category.