Four-part answer: (1) Used to it from playing lots of WFRP4; (2) Players liked it in WFRP; (3) One less roll, so why not; (4) d20 is for that other game. :-)
. What’s gained - see above. Hitting a right leg is 01 - 15, so the following hits would land blows there: 01,10, 11, 20, 21, 30. 31...