Do players just associate bigger numbers with being "better" in some way? Is there some cultural factor I'm missing? Is this just a way of saying "I don't want to play any game that isn't like D&D"?
I've asked a few hundred 5th and 6th graders over the years which was better. By that age, there's a strong trend even in the abstract.
About half said higher, and IIRC, about 1/6 said lower, The rest were largely don't care, with a few "i don't know" and "Not understand question, Mister H." (Ah, the joys of teaching severely low-English-proficiency students.)
The RPGers I knew prior to moving south were about 2/3 higher, 1/3 lower, but more importantly, 1/3 won't play a roll low.
Down here in Oregon, the kids I run for now, none are "won't play roll low". I've only met a couple "won't play roll high" types ever. (And neither was autistic. One only played Hero System; the other only played BRP.)
More interesting is that the roughly 60 4th graders asked "Which do you prefer: roll high to win or roll low to win?" - it was maybe 1/3 roll high, and the rest didn't care. And one, very sharp, gifted ed student, responded with, "Math says they are the same. [boardgame] says higher." (I don't remember the boardgame - but it was one of the Parcheesi variants. Not Sorry! nor Trouble, but one of that ilk.)