If "it isn't in reality any safer than not wearing one" one has to wonder why professional bicyclists engaged in a race like the Tour De France always wear protective head gear.
Because they're going really fast, often in tight bunches, often on windy roads, on really skinny tires.
Whether or not helmets increase safety is probably case specific. It is probably a small subset of riders that have an elevated risk of accident that would benefit from a helmet.
It seems fairly clear from the data that on average helmets do not increase safety. This is likely because among casual and commuter riders the risk of an accident that would result in head trauma is actually pretty low. Sure if they do happen to fall in a way that they smack their head on the curb then a helmet would have helped. But the actual rate of such injuries per number of riders must be pretty low.
There's a big difference between grinding out 50 miles on the back roads of Volusia and Lake Counties at 20+ mph on a skinny tire bike with roads filled with rednecks and blue hairs that think I shouldn't be on the roads in the first place and me riding my beach cruiser along Rockledge Drive where the speed limit for cars is 20 mph and there are gobs of riders and pedstrians such that cars expect you to be there and respect your non-motorized presence.