Not sure hot to explain why...its just how the odds work :P The amount of straight and flush draws possible increases the odds.

910s is favored over 22-55 at a similar rate, and then at 66+ the odds decrease more, because you are removing outs that would complete a straight for 910. Same thing with J10s...this is also why 22-77 are less likely to win, and 88 is more likely, because it eliminates more straight possibilities.

This is also why J10s is favoured more heavily over an underpair than AKs is...there are more straight possibilities.