Lots of "luxury" housing is made with crap materials by unskilled freelancers. There is a ton of skimping on hidden details like missing flashing around doors and windows. You can't trust any home built within the last 25 years.
In my case, the insulation was mostly just air. There is zero insulation at all in my garage in a place with harsh winters and there is no insulation between my garage and the house. My attic also did not have insulation, but that one was cheaper and easier to resolve than all the wall cavities.
Unfortunately we aren’t the first owners. I know some of the issues we are seeing is from shitty diy or contracting from the previous owner, but most of them are from the original construction. One example of shitty DIY is the hardwood floor on the main level that we are currently replacing. The newly installed floors were a bit lower than the original floors so they just covered all the gaps with corner round all around the baseboards. Looks super tacky. But is a fairly minor issue all things considered. We are replacing that with another layer of sub flooring and engineered wood floors to try to reduce the amount of movement you can feel in the floors.
What are you talking about?