I'm sure there is a reason. I'm guessing it's banned by the rules. But I don't see where in the rules that this is banned. Will be great if anyone can enlighten me.

Rules I checked: https://pastebin.com/VtzvMpyW

Example speed run (P5 NMG #1):

The inventory scream skip:

For example, Soul Tyrant's scream wasn't skipped in the above speed run. However I just tried on my xbox that the inventory skip can be done with my dumb hands and get in at least one hit, so I imagine multiple hits in the hands of a top speed runner.

Thats because this counts as a major glitch, because it uses inventory storage.

Thanks for the reply, KC_Speed.

I tried to understand the major glitches (I noticed inventory storage), but didn't find a guide for such explanation.

Is there resource explaining what each major glitch looks like and how they actually work?

NVM I found this guide which isn't mainly for this purpose but did explain the concept of "storage" in its FAQ. https://www.speedrun.com/hollowknight/guide/4e1dp

FWIW, for the benefits of new comers, I wished there could be one single guide to explain the rules and the glitches in finer detail (and made easier to find).

OMG that would make collector so easy!!!

For Collector, I do see top runners dash into collector before screaming, so that they take dmg during screaming and be able to attack. This is legit (as in "not a major glitch"), btw. But seems to require good timing (e.g. I get 1-2 out of 10 when I try it).