My argument applies to reinforced masonry as well. You seem to be operating from a naive model of what is required to prevent combustion of buildings. We already use non-flammable walls in a lot of places; it is a speed bump for a serious fire without a lot of additional mitigations.

Most typical reinforced masonry will fail during a severe earthquake, for which there is ample empirical evidence. The cost to reinforce masonry to e.g. a M8.5 standard is not small. The quantity of rebar, ties, etc required is expensive in both time and material. It isn’t cheap nor does the labor exist at the scale required.

I actually live in exotic construction, designed for extreme seismic and wind loads. Lots of steel, not much concrete, and extremely fire resistant (even though that isn’t a requirement here) but much cheaper to build and more seismic resistant (in theory) than reinforced concrete, which is what it replaces (its raison d’être). No structural wood either, but it wouldn’t be economical to construct a typical house this way.

This is an active area of research. If it was an “urban myth” there wouldn’t be so many engineering firms investing in developing new construction techniques that provide seismic resistance without the cost. If reinforced masonry actually worked in a reasonable way, we’d just use that.