[kragen]

That's one possibility. Another is that it has a critical drawback; Masonite siding resulted in a massive class-action lawsuit verdict due to moisture damage (though the researchers say Superwood is less vulnerable) and it occurs to me that maybe structural steel's plastic deformation when overloaded as a construction material is somewhat more forgiving than the brittle fracture behavior typical of wood and evident in the photos of their ballistic testing.

[littlestymaar]

That it has a fatal flaw is indeed a possibility, but I don't think it could be the reason why it hasn't been invented sooner: if anything, we are detecting these kinds of flaws way faster than we used to, so it's likely that in the past it would have been produced at scale long before we found the problem, and given that consumer laws were nonexistent back then, it could have been kept on the market long after the flaw had been found, as long as it is economical enough to produce.

[rascul]

I've worked with masonite too many times. That stuff is garbage and doesn't belong anywhere near a house.