Why does everyone list IV as a percentage?

because the different IV calculators all give a percentage instead of a total, so it is easier to use that number given instead of taking the small amount of time to add up each separate IV number.

Who wants a 45 perfect poke when they can have a 100% perfect poke? :)

Raw number would be more precise and overall better.
Nevertheless everyone started with the percentage system and renamed their pkmn with --%; Changing "system" and renaming every single pkmn in your box is percepted ad boring and a loss of time, so people stick with %.

In my opinion, 44 or 97,8% are the same, it only matters if you break the raw number to 15-15-14 or 14-15-15 as the last CP of your pokemon will be different in this case.