I don't get it
Gasly swoped his helmet (Chinese, France, Hubert & Japan) 4 times this year (not included switch RBR to STR)
Kvyat one time (Monza looks almost his normal helmet design) and he may not do a swop
Verstappen 3 times but this is valid because sponsor reason supermarket JUMBO(Yellow)
From what I understand, if the change is relatively minor, it's usually allowed. It's only the full scheme changes that are limited. Personally, I wish they had freedom back again. I used to like Vettel's helmet designs a lot.