Nilopilo -->
That's mainly because the punch parry isn't as good as the regular parry.
The PP deals more damage, but it's worse on whiff - the steve player knows that the Law sometimes parry, and if Steve fakes it and the Law does the punch parry, the Steve will be ready with the sweep.
If, however, Steve fakes it and Law does the regular parry, Steve won't have time to punish with the sweep.
Instead, Steve would have time to do a launch, but then he wouldn't have time to punish the punch parry with a sweep (Law can jump over with PP~dragon kick if the sweep is too slow) if the Law instead made the punch parry.
You can see examples of this in me vs Sakis, sometimes I do the regular parry and sometimes the punch parry - he never had time to do a launch when he punished me, which is exactly what Law wants when he mixes the parrys up

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But there is another reason the regular parry is used more often, and that is because it's faster.
These videos are from a tournament game and we both played quite shit and we were both very dissapointed about loosing in semifinals (never lost a set to chef before that semifinal ^_^), so when I saw his 4~2 (I don't know exact input, but it's the launcher where he sways to the side and then does a heavy uppercut with mad range... -13 on block, but unpunishable), I didn't want to risk doing the PP since it activates slower, it's easier to just do the regular parry. Also, when Steve does df+2, it's _VERY_ risky to try the punch parry on reaction, but the regular parry is quite easy so that's a better option in that situation.
The third reason the punch parry (and a lot of other stuff with law/heihachi) wasn't used by me there is because I haven't really played law or heihachi for quite a few months (after I qualified for swedish nationals my law/heihachi usage percent turned single digits), so I've stopped doing the "advanced" law/heihachi stuff, like adjusting myself to using punch parry instead of regular. Also, after punch parry~2 I like to do forward forward+left kick, but because steve is so gay the angle after parrying a lot of his stuff makes it whiff, and noone ever ducks the duckable last jab of the DSS+2f2f2 after I do regular parry so I figured I'd just do that one instead ^_^
Sorry for the long answer to a short question ;D
thanks for the props
HYULVINJIII --> what does "Sjelden en ser ensformighet i en så spennende form " mean?
"Its rare to see repetetive stuff that exciting" or something?

sorry for my 221 spam, as I said I havent really played hei for a long time

all about kazuya.
I think more vids might come later, but it's the chef that has to distribute those.