At the price of an eSIM and a LTE modem (and of the stolen 100$M), destroying a glued casing and making your own costs next to nothing. Looking at the photos, even without the test pads soldering directly on the components seem pretty easy.
Last year there were ones going around with these eSIM modules in them and they appeared to have printed new 3D cases for them, so it's definitely something they have experimented with.
Even if it is still possible to do, doing it at scale becomes a lot more complex