What some see as a natural progression in technology others see as heresy
Usually the UCI who see things as heresy..
That's why you're still riding a cycle designed in the 1800s, not one designed more recently.
Carbon is a material that isn't well understood by many - we have regular experience with metal, not with composites.
Making a bike that masses 3kg is all well and good, but it's probably only sensible for hill climb events.
horses for courses as they say - for an everyday transport vehicle a few extra grams and the ability to take a knock on the bike rack, as well as various tyre choices, full mudguards etc. are much more important than the material...
Mr Burrows has been using CF for quite a while, and is producing some rather marvellous looking 'everyday' machines in the stuff - structural chain case, stub axles, no top tube, so nice low step through....
The UCI would have a fit, but I imagine there is enough additional carbon on these to help support the frame in the event of an inadvertent knock or two.
The danger is that CF can fail in ways that aren't visible, and so you can go from 'happily riding' to 'moving above the ground with a collection of components loosely bound' without obvious warning.
No doubt such failures are exceptions, but the tendency with steel (for example) is for a failure to propagate, and the frame to 'soften' before it fails...