I think the 6-9 are better candidates (and I have reasons) but I'd really like to know why the 2-5? Hell, why not the 10-K?
Weird question considering that game was invented by some successful and rich Chinese businessmen in order to increase the likelihood of getting strong hands and to gamble more as they probably got bored of folding so much in NLHE. Obviously picture cards are more fun than playing with 2-9 for example.
The story goes that a Macao businessman was sick of running into low sets and 2pair and cracking his AK so he threw out the small cards, so 6+ was born Im not sure how true that story is but that's what Tom Dwan said. At least it's a good legend