Well as someone pointed out, motorcycle/scooter turn signals arn't that much farther apart and work effectively.
That's true, but on the bike I'd want to differentiate a turn blinker and center hazard blinker as much as possible and remove any ambiguity about what the blinking light means. Motorcycle/scooter lights are more powerful, too - this set can't be very bright. If you could run these as bright as a motorcycle set, and have some additional hazard blinkers to differentiate yourself from a motorcycle, that would work fine.