I mean, sure there are plenty of liberals who are willing to critique capitalism since they want to make it better without removing it, but it's easier for someone whose whole platform is based on "I hate the rich and the 'billionaire class' and don't want their funding" to argue about the fundamental flaws of capitalism and why it needs to be replaced with a new system than someone who is fine with millionaires and the existence of capitalism.
But Bernie is really a social democrat and not a socialist, so he wouldn't go that far. That said, by virtue of positioning himself as a radical candidate, he should/could have been the one to not just make a reformist but a more radical critique of capitalism. Kind of like how Coates was annoyed because Bernie wouldn't support reparations - it's not that anyone expects that he would, but because he's selling himself as a revolutionary, he really should be able to say these things. And it would show that he has a deeper, more intersectional understanding of both capitalism and racism than just "Wall Street bad".