It's not. I thought the definition of a dice pool system was counting the number of "hits" and not adding up the numbers and comparing that to a target number - which is what GURPS does. From what I can see posters are mixing things up.

Actually, the definition used more generally industry wide is where the number of dice is dependent upon character ability scores.

Some, such as D6 System, are roll-and-total.

Some, such as Prime Directive 1E and LUG Trek are keep best die, with a method for explosive.

Some, such as Shadowrun and Vampire, are count successes.

ANd then, we have the "Roll and Keep" pools...

Roll x dice, keep y of them, then total those Y dice: L5R 1-4, Cortex Plus, Savage Worlds

Roll X dice, keep y of them, count the symbols: L5R 5e

Technically, Savage worlds is keep 1, and is at most roll 2d keep 1... but the dice rolled are 1d6 & 1d(skill).

Cortex plus is almost always roll 3-8 dice, of size by ability and inclusion if relevant, keep 2.

L5R 1, 3 & 4 is roll Stat+skill, keep stat. 2E is roll Skill keep stat. Both cases, total the kept, compare to opposed roll or TN as appropriate.

All of those use character skills and/or attributes to determine the number of dice to roll.

Symbollic Dice Pools include WEG's DC treatment ....

1 wild die, skill-1 other dice. Wild -1, 0, 1, 1, 1, 1, 1+Exp; other: 0,0,1,1,1,1.

Really not much different than the roll and total approach, just reducing the numbers.

FFG WFRP3 - Way too convoluted for here, but multi-axis results and always a chance of success and of fail.

FFG Star Wars: much more streamlined with only 8 symbols, and 7 kinds of dice, and simpler talents as well.

FFG Genesys: different advancement, but otherwise, 99.9% same mechanics as Star Wars - the exact symbols changed, but the names and rates are the same as in SW.

FFG L5R - even more streamlined, 4 symbols, two dice types, fixed number difficulty, and sometimes a no-chance roll.

All of these are variations of dice pools. What dice you get is by abilities....