The problem is that as another commenter points out, passengers wouldn't feel safe next to a helmet-wearing driver while not wearing one themselves.

The proper solution here is to provide helmets for passengers as well, but that raises more problems - they needs to be a way to sanitize them, multiple sizes might need to be available (I assume they need to be sized properly for adequate protection?), etc.

The aforementioned problems are hard (read: expensive) or impossible to solve, so while the ethical idea might be to just not offer this service at all, the objective here is to make money whatever-it-takes (or most likely, raise money, as I doubt this thing is profitable) as opposed to providing a good transport service (maybe because there's no actual demand for this?).