A cushioned cardboard box is enough for a newborn. Its weakness could be moisture and high flammability. But aside from that it is perfect.
These two things seem to be connected. In my experience infants get more flammable as they get drier.
The flammability is even more strange. Again yeah, maybe don't put your baby box right in from the of the fireplace, but you probably wouldn't leave your baby there unsupervised anyway. Also babies usually aren't smokers so you don't have to worry about them dozing off with a cigarette and burning down the house.
What’s missing is that lots of things in your home are bad in water and are flammable. But how often do you need to save a baby from an evil villain by tossing their little box into a river and hope a nice childless couple who always wanted a child finds them and raises them as their own?
Situations where the material is a liability are few and far between.
Maybe this fear explains the popularity of the Moses basket
https://www.google.com/search?q=moses+basket&client=ms-andro...
In fact, with imitations of the maternity kit (or just the box as a sleeping spot) becoming more popular outside of Finland recently, often boosted by marketing playing on the correlation of the kit and the decline in infant mortality in Finland, a number of health entities in recent years have raised concerns that the box-as-crib itself may be a safety risk rather than an aid.