Is the world becoming uninsurable?

Not uninsurable, but buildings are going to have to become tougher.

It's happened before. Chicago's reaction to the Great Fire was simple - no more building wooden houses. Chicago went all brick. Still is, mostly.

The trouble is, brick isn't earthquake resistant. Not without steel reinforcement.

I live in a house built of cinder block filled with concrete reinforced with steel. A commercial builder built this as his personal residence in 1950. The walls look like a commercial building. The outside is just painted cinder block. Works fine, survived the 1989 earthquake without damage, low maintenance. It's not what most people want today in the US.

If the market is allowed to price insurance correctly then we can motivate building designs to be more disaster resist. If the McMansion can't get insurance but disaster resistant, modest homes do, then people will adapt.

It was only a week or so ago that I learned that a major failure mode of most houses in Florida during Hurricane season used to be the roofs ripping off. The tie plates and straps that were invented to solve that problem created the McMansion as a side effect.[1]

[1] https://www.youtube.com/watch?v=3oIeLGkSCMA