Mild steel becomes ductile at relatively low temperatures, way before it actually melts, hence why you sometimes see steel beams deform and drape over timber beams in a fire. The ductile transformation happens relatively quickly once you get to the critical temperature on the iron carbon phase diagram for typical construction grade steels. Hence why Steel is usually protected with fire rated drywall like boards, intumescent paint or weird spray on insulation that looks like porridge.
Whereas with timber the rate at which it will burn is reliably predicted, so exposed timber structures are designed to be oversized so that the reduced beam sizes will still be effective. This is done using a charring calculation to give the required amount of structural integrity duration which varies depending on how tall the building is and what it is used for.
All types of structure will fail eventually in a fire, the assumption is that the fire brigade will tackle it before it goes too far.
In the UK, the main fire related problem with CLT is that the exposed surface doesn't meet the requirements for the speed of surface spread of flames so it has to be treated with a fire retardant or you need sprinklers if you want to expose the material. Both of which are expensive.