I didn't take the time to read all the other replies (just scanned them abit), so I hope this is not redundant.
The first thing I thought of, and this depends on your Mom's age, is that some parents who lived through the Depression, even as kids, have this mindset that you can't go "throwing money away" on things like WDW. Maybe she's just worried about the money. But of course, if you're looking for codes, I'd guess you look for other ways to do WDW cheaply (us, too), so there's no guilt there.
And if it's not the money, but the fact that you go to the same place a lot, it's like a lot of the other people have said: Many people take vacations to the same place every year.
If your family (or even just YOU) loves to go somewhere, and being there makes you happy: DO IT!! I'm heading out soon with my SIL, who's never been. Between us we have 7 kids, 5 of whom are 12 -17 years old--Boy do we need a break! Sometimes grown-ups need a chance to experience the freedom and magic that come from being a kid again, with or without the kids!
It's sweet, safe, clean, happy, and youthful. The service is top-notch, the variety of things to do is perfect for families, and the sunshine is what I personally need for my sanity!
Hooray for the Mouse, and hooray for those of us with the ability to find joy in sharing sweet and innocent times with those we love!