To be fair, the flashing on bicycles is intentional, precisely to make sure you are aware of them, since they're so much smaller and vulnerable, and the light itself is so much smaller than the rear light on a vehicle. It's not just on rentals, it's a standard feature of bicycle rear lights that is there for safety.

Flashing lights on bicycles are illegal in a lot of places.

If bikes didn't move, a blinking light would be fine. But they do move and it makes it really hard to tell where the bike is in the dark.

In the Netherlands, bike lights _must not_ flash. The law very explicitly states that they need to be "always on" (in the dark).

The main reason seems to be that it's hard for others to to gauge your speed when your lights are flashing.

Blinding and dazzling oncoming traffic in the name of safety is outright stupid.

If you are riding a bike and you're lighting up the heads of oncoming riders or pedestrians you are being dangerous and obnoxious. Never shine a flashlight above someone's shoulders at night if you can help it.