Yeah, in the old days a driver would have a helmet design that would pretty much follow him for life. That began to slide in the 00'ies and Vettel amongst others took it to a whole new level with new helmet designs at every race. The showmen were afraid that viewers could not recognize the drivers when the constantly had new helmets, so the different helmet design once per season rule was made. Now that we have clear markings of both numbers and driver initials on the car, it kind of seems like this rule is obsolete. But don't expect it to go any time soon.
It's only after we've lost everything, that we are free to do anything.