Survivorship bias: you don't see the shoddy homes from that time period because they didn't make it.

More likely the quality of wood and carpentry is higher. You can't buy wood these days, certainly not economically, that compares with what was standard 100+ years ago.

Yup. Most studs and beams were made of far better would than the short growth wood we have now. Heck, there are firms that specialize in recovering old wood from barns and factories since the wood is so much denser, and the size is simply unavailable elsewhere.

Huh? People used lead paint widely, and many 100+ year old houses were painted with it.