nluv, exactly.
My guess is they ran the numbers and found that enough more people chose WDW in off-season, and per-person spending went up (shopping, extras, ticket add-ons) due to getting such a big freebie, that it was enough to even out the food-loss.
In the restaurants alone, people drank more (big profit item!). Adults who wouldn't drink or might get one and split it, were ordering a couple. In shops, toys and clothes and collectables were more readily purchased ('we just saved $200 on dinner, so I can buy this $45 sweatshirt I want', etc.). Upgrading tickets to add water-parks, or no-expiration, etc. Keeping people on Disney-grounds for most all of their vacation. And don't forget everyone paying full price for the room vs. discounted by
AAA or room-only discount deals.
My fear was that menus/quality/portions would be adjusted to help the free-DP not lose much, but that didn't seem to be the case last year. There may be some small adjustments, but probably not that noticeable. The fact that they're doing it again means it worked for them on macro level. I mean, my family is going back again this year and we wouldn't have w/o the free-DP.
Viewing last year, I hoped and sorta suspected they would do it again. If people enjoy spending a little more elsewhere due to the free-DP, then they'll probably bring it back again after this year.
I'll see you there! (We'll be the ones gaining 8lbs. every Fall

)