Untrue. Even small communities have shown to be able to do maintenance on whatever piques their interest. 250 customers with a high stakes product is large enough for them (or their insurer) to collectively hire say one programmer and one mechanic. That would be more capacity than 50% of FOSS.
You're perhaps underestimating vision scientists. If the problem is a driver (or something else that doesn't require a surgeon), I'm not the only person who might volunteer to develop the driver, given the alternative of people returning to blindness.