The risk is drastically less, as evidenced by the crash rates and crash severity.

Is it? Vic Roads claims you are up to 10x more likely to be killed if you travel by bicycle vs car. And it would make sense to me that you're more likely to be killed if you ride fast. Certainly all of my own bicycle crashes have involved speed - I've never suffered any injury at all, not even a bruise, when I was riding at a leisurely pace.

Your claim that there's no risk to cyclists is clearly wrong. Injuries when a cyclist hits another cyclist or pedestrian are severe.

It would, obviously, be ideal to separate pedestrians and cyclists so they don't share the same bridge. Or make the bridge wide enough to have separate lanes... But in the real world that's those just won't happen and it still doesn't help with crashes between two cyclists - which are a lot more likely to happen when you have a mix of fast and slow cyclists on a narrow bridge.

But anyway, I generally reject your assertion that the punishment should be matched to the level of risk. For me the punishment should be set at whatever level is necessary to encourage the majority of riders to ride safely. And it's not up to the police to determine what speed is "safe". That determination is up to the town planning contractors who set the speed limit on the bridge.

If it was a slap on the wrist fine, everyone would ignore the speed limit. That doesn't seem right to me at all.

None of the bridges on my commute have speed limits. When I cross them I generally do drop down 1st gear and ride at less than 10km/h (and my bicycle does have a speedometer, so I know I'm going less than 10). If there are pedestrians I slow down to walking speed or even stop while they walk past. Why risk hurting someone? I'm not in a hurry.