Clearly they didn't know how to build things very well. Crystal Palace type structures look impressive, but they are _bad buildings_, both in terms of practicality (what would you use one for?) and safety, and no competent modern engineer would design one, even if it were legal, which it is not. There were a bunch of things like the Crystal Palace built in the 19th century, and the reason you don't see many these days is that they mostly burned down, often within a few years of construction (the Crystal Palace was actually an unusually long-lasting example of the genre, likely because it was mostly lightly used or completely disused).

Like, "why are more people not building impractical fire hazards? It must be because people these days are incompetent" is a pretty weird take.