The reasons
I also know people who don't get Disney World even after being there, and here is my list of theoretical underpinnings as to why they think that way:
1. They are extreme penny pinchers who can't get over the fact that things cost more at Disney than at home. In short, they can't stop worrying about the money, and they know they can have a "vacation" somewhere else cheaper. Yes, it's pricier, but it's worth it.
2. They hate crowds and standing in line. Suck it up, or go somewhere less crowded for a while. Also, go during the slow times of day, like mornings.
3. They cannot walk great distances because of ill health, unfitness, or laziness. Get in shape, or get an electric wheelchair thingie.
4. They had bad weather while there. Face it, if it was raining or 108 degrees all day everyday you have been there, you wouldn't like it as much either. Usually the weather is great, try it again at a different time of year.
5. They never saw Illuminations or Spectromagic. Stay up a little later and do it. It could make it all worthwhile.
6. They are not "magical" people. They simply don't see the wonder of it all, and how the rest of the problems in your world disappear when you are there, or they continue to call work everyday while there. Find your inner child, and forget about work for a few days. They'll survive without you.
7. They are gloomy, depressed people in general. Stay away from them, they can suck the joy of life right out of you. See a therapist or get a prescription for happy pills. If not for your sake, then for the sake of those miserable people around you.
8. In efforts to save money, they stay off-site, pinch pennies at mealtimes, and don't take the kids (if any) back to rest in the room for an afternoon break. Misery and time-wasting ensues. Stay on-site if you possibly can, and take a break. Almost everybody could use a break in the afternoon.
9. They don't plan or do their research, so they go at the worst time of year, fail to learn Fastpass, stand in line for the wrong things at the wrong time, go to the wrong park on the busiest day for that park, and generally have no clue about how to maximize the fun. They also fail to take advantage of the short lines in the morning, insist unsuccessfully at trying to eat during peak mealtimes, fail to grab a spot for the parades, and leave before the fireworks shows. Read this website, and get a couple books at the bookstore or library. A touch of flexibility also helps.
10. Their idea of a vacation might be fundamentally different from yours. For example, vacations for them might be the following: driving 800 miles a day to cover territory while seeing almost nothing, drinking, gambling, seeing old friends and relatives, staying at the homes of old friends and relatives to save money, doing naughty Vegas stuff, sitting on your butt by some water in a languid pool of inactivity, or being uncompromisingly selfish to the point of complaining if everybody doesn't do exactly what he or she wants them to do. Adjust, shift your paradigm, and enjoy a truly classic vacation for a change.
Oh well, these are my observations for what they are worth. Yes, there are a few people I greatly like and respect who do not jump for joy at Disney, but they are rare. Most of the people I really like enjoy Disney a lot and "get it".
You may find that the same people who dislilke Disney also complain about Christmas shopping, decorating, cookie making, etc . . . Christmas and Disney are similar in that there is a legitmate spirit to both. Of course, some people who don't like traveling may love the home Christmas spirit. They may also have a different religious background, but that is neither here nor there.
Nevertheless, it may be interesting to poll the correspondence between Disney and Christmas lovers.