For us it's the quality verses the price. I've had some pretty lousy TS meals at WDW over the last two trips. And when I look at the bill for that pretty lousy food, I figure it's not worth my time, the effort and definitely not the money. So add insult to injury and reduce portion sizes on good food and I figure I'm getting my eyes ripped off.
Everyone's taste buds and expectations are different. I expect a level of quality verses a price. And I don't care if I'm paying for location, location, location. I expect a premium but not enough to make my head spin. And recently, my head has been spinning.
So we're doing a lot more offsite dining and expect to continue to do so the next time we're there.
Oh, and I don't buy the "well, it's better than other theme park food" argument because people don't eat WDW food for one day the way they would at a ballpark or a Great Adventure. It's a several day vacation for most people and it's obvious that WDW is trying to keep patrons onsite as much as possible. With that in mind, they should make people WANT to stay onsite for meals. I'm in the minority, though, so I don't expect people to agree with me.
One last thing.....if they can break even or make a bit of a profit from DDP as some posters suggest, then how much are they making on the OOP patron? If you order a full three course meal at a TS restaurant and nothing else all day, your cost is significantly higher OOP. Even if you only order one TS course, a CS meal and a snack you're making out albeit by a small amount. So how much is WDW making on the OOP guest? It's astronomical. Reduce portions and quality and it's just a blatant rip-off. JMHO.