Modern houses are far more complex undertakings than houses built a decade or two ago. This translates to cost.

Take a look at something like the BC Energy Step Code https://energystepcode.ca/ and its guidelines on thermal bridging: https://www.bchousing.org/research-centre/library/residentia...

It produces better buildings, but this is all new and expensive. Expand this sort of thing all out to all the other components (electrical, plumbing, foundation, etc) of modern, compliant buildings and you get the idea.