Descending into HKoholism
Here is the link to the model for USP: https://grayguns.com/product/hk-usp-hk45-short-reset-system/So, why don't the USP an VP9 need short reset parts? Oh, because they were designed right the first time.
In my limited experience, HK45 has the shortest reset compared to USP, P2000, and P30.
As for VP9, it works on entirely different mechanics (striker fired), and if a system to shorten the reset is designed one day, it will have to be completely different to match that.
Unless of course, you were asking a rhetorical question.