Steel has a better failure story than carbon fiber. Many impacts that would shatter a carbon fiber frame, dangerous to the rider, will only bend a steel one. Carbon fiber makes sense for a racing bike, but for street riding I'll stick with steel.
A friend of mine was nearly killed on a carbon fibre frame that just tore itself apart while going up a hill and threw him into the road, unconscious. I would never touch one for street riding.
Carbon fiber frames can be challenging to see the cracks and damages to it before it spectacularly fails. There's a good chance you won't know it is about to break until it shatters.
Any material under stress gets fatigued. The problem with carbon fiber specifically is that there are practically no visible signs of it reaching the threshold.
I don’t know how common it is, but why would you take that risk on the road for a couple kg of weight savings? If you’re racing competitively that’s one thing, but is it worth it on the commute?
