The most notable factor is the final noted factor: nostalgia, as many collectors will spend higher quantities of money to purchase cards/characters that were important in their childhood
There are Fighting-type Pokmon (which include Fighting, Rock, and Ground-type Pokmon from the video games), like Machamp and Onix, and Fighting-type attacks
The only exeption for this are Premium series like The Best [PRB] with 10 booster packs per booster box
Gen 2 Card Reveals, Meet & Greet Schedule, Trade Night Box Breaks, and more
Invoke Prejudice, largely due to the card's artwork (which depicts persons who bare a close resemblance to members of the racial hate group Klu Klux Klan)
Know what strategies you're likely to run into and have a plan for utterly dismantling them