Because it's a stupid term that doesn't make sense
Alright, check yourself, Mr. Hot Shit. It makes perfect sense.
"Full price" is relative to the product. It means, more or less, the widely accepted maximum retail cost of the item. For most AAA current gen games, that means $60. If it's a lesser game, or whatever, the retail price will be lower. Or, if it's some special edition or whatever, it could be more.
Basically, "full price" means...the most money that particular game would ever cost.
OP is implying that most games he purchases have been discounted from their original price.
It's not tied to one specific dollar amount.
Which would make zero sense as a claim because I have seen many people brag about this You want to tell me they never pay a $10 for a indie game that was not on sale?