Then they'd be to busy in stop and go traffic reading it and thinking about it while talking on their cell phone & eating and slam their silly useless vehicle into you.
I can't think of any other reason why you can't go for brighter bulbs, just don't get crazy and melt something though. What would be nice is if you could find yourself something with about the same wattage in dim mode but brighter for the brake filament. I once was a click away from ordering all LED brakelights but never did because of this issue, and yes my CC works perfectly.
The thing about LEDs is that they are much more vivid, but no where near as bright as regular bulbs. Most LED lights also don't use the reflector very much, it is mainly what shines straight back.