As a pp mentioned, they are getting cheaper dining dollars out of the DDP people. That's one reason we were already buying the DDP prior to getting it on the
free dining plan- we were lucky, the dates worked out for us (another benefit of homeschooling). But, we're also paying RACK rate for the resort for 2 weeks. They may not be getting my dining dollars this year, but they are getting my resort dollars - this year at a moderate, for the last several (as in 8) years at deluxe resorts.
I do empathize with the OP to an extent. But, we live in Louisville, KY. It doesn't compare to Disney (either size or crowd wise), and I know that the little known KY Derby is only about a month's worth of festivities, but forget hotels, restaurants or driving in Louisville during most of it and especially for the weekend of the actual Derby. We know and love what it does for the city (I've never actually been to the Derby itself - many locals haven't), but we simply know that during the month when all the events are going on, to travel further afield if we want to go out during weekends and many evenings. It's part of the city and you either live with it or go crazy.
We have had family/friends come to town and want to go out and enjoy the festivities, but unless they've planned ahead (and yep, hotels book more than a year in advance for the Derby, along with many top-line restaurants), we drive 40-50 miles away to Lexington to dine there (unless of course, that there is racing at Keeneland that weekend, which means we go a different direction).
It's all relative. WDW wouldn't even have the scope of restaurants it does if it weren't for the tourists. Along with that, there will be headaches for the locals. I'm sorry for the inconvenience it causes, but would I stop planning my vacation to ensure that we can enjoy it to the fullest so that the locals won't be inconvenienced, nope. Sorry. It's once a year for us and we plan to enjoy every minute - or we wouldn't be coming. Would I have a problem with Disney holding out a few tables for last minutes or locals, not really. I just don't think a business will hold empty tables in the hopes that the right demographic (i.e. locals) will fill them up every night. They'll go with a sure thing and in this instance, it's tourists.
Not fair, and sympathy extended. Wish there were an easy solution, but I just don't see one. Maybe the WDW people will see this thread and consider some local specials to help alleviate the problem sometimes. Just like they set up the DDP for certain weeks, they could set aside certain weekends with an emphasis on locals. Might be a solution there somewhere. Good luck!