Very funny to see in what I assume is a million-dollar product.
Of course random arduino module and teensy used for product is amateur hour, even for low volume production. They must have crazy margins on that camera and producing custom board is very cheap.
It's expensive in time and expertise to do a custom board, and to debug a custom board. All to what, save 20$ on a bom which might not even be 1% of the profit per unit?
Far more efficient to just ship the dev board. They could have perhaps picked a better dev setup to start with, but if it looks stupid and it works...
Unless they are making literally less than 10 of those, custom board will be easier to manufacture than that mess of dev boards and more reliable than random wires and headers all over the place. Plus they can spend money where it makes sense, using better regulators etc.
Speaking as someone capable of designing the mechanical hardware and who is broadly electrically savvy but who is most definitely not an embedded engineer: I could bang out a few hundred hacked together dev boards in week, but doing a custom board would take me a few months. Starting with reading 'Prototyping PCBs for Dummies'.
Watch a few YT videos, copy-paste the reference schematics for all those boards, delete what you don't use and you are almost done :)