From personal experience (and a
lot of it...)
Reason number 3 -
Complete and utter literalism - I went with a coworker to a pizza resturant for an "All You Can Eat" buffet. There were a lot of different pizzas avilable, and salads, pastas, etc. I entered and looked around, planning where to sit, finding the restroom, etc. and noticed the sign for the lunch buffet customers: 1)Pay cashier 2)Take tray. When I did those two things I sat down. And waited. Nowhere on the sign did it say to get food.

Once clued in, I did enjoy a nice lunch. The price was reasonable, and the food served it's purpose...oh wait - sorry.
Reason number 2 -
Boring - I admit it (although probably more so for the I vs. E). When I took the entire test (there were about fifty of us at the time taking it, IIRC), the administrator then showed type differences with role playing, etc. She asked for anyone who scored above 80 on the "I" scale. About six or seven of us stood up. She then asked for those who scored over 85. Two of us were left standing. She asked what our scores were. Again, IIRC, mine was about 95. Similarly high scores for S, T and J. The adminsitrator didn't use me for an example after the second time because "his answers would just be the same." Heck, I thought that was the point.
And the number 1 reason -
wait, what exactly is the criteria for "top three"? Each individual's top three reasons, a collective vote on the top three reasons, top three from SJ's themselves; how can you call a list "top three" without some kind of objective criteria? Reading the posts from the start it seems like "top sixty-two" or something. Can the thread be renamed?
Anyway, just my thoughts.