The ductility of metal has been a tremendous boon to fabrication of large machines. If parts don't quite fit, they deform to fit. This caused problems when carbon fiber started to be used to build large airplanes. Those parts don't bend and retained the internal stresses caused by mismatches. I read this happened to Boeing.

Glass and ceramics are harder than steel. The reason that glass is fragile, is that one can use its own strength against itself. The material itself acts as a lever to concentrate enormous stresses at the tips of fractures. This doesn't work nearly as well when materials are ductile.

Disclaimer: not a materials guy.