Everybody knows that nobody wears a helmet while riding scooter company. The manufacturers know, the ride-sharing services know, and the riders know. But if a helmet warning is clearly displayed, that gives the scooter company virtual legal immunity from injury lawsuits.
Even if the scooter's unsafe with a helmet, the situation prevents any serious legal damages. Only a small minority of riders will actually wear the helmet, and the company can just settle with on an individual basis. This pool is too tiny to attract high-powered class action attorneys.
The vast majority of riders, and therefore injuries, will be helmet wearing riders. Proving the counterfactual that they would have sustained the same injuries even with a helmet is very difficult. Head injuries by far are the highest damages, so again the pool of non-head injuries is too small to attract serious class-action attorneys.
A good lawyer could argue that riders do not know they need to wear helmets on the scooters.
The Dutch do fine riding bicycles without helmets.
If scooters are in fact more dangerous than bicycles, we should probably just reevaluate their use in the first place.