They try to make up for how poorly the walls are constructed by shoving tons of insulation (mostly hazardous-during-deconstruction fiberglass) but really it is just nothingness. I'm sure with a wood axe I could literally chop my way into someone's bedroom from outside.
In much of Europe both new and old homes are built using brick(!). These homes have already lasted over one hundred years and will likely last at least another fifty or more with normal maintenance (e.g. roof repair, replacing some plumbing, etc).
Most US homes seem to have a lifetime of around 50 years before they get demolished and replaced by identically terrible homes. Except there are a few places in the Eastern US where older homes were built well (e.g. Maine) but newer ones are built like junk.
I'm not surprised they're bringing in building materials from Ireland. I doubt anyone in the US produces real homes anymore.