Supply chain/production complexity. It's more expensive for them to make the option customizable than it is to ship it for everyone. If there was an appreciable market for consumer-level camera-less machines the math to justify it might look different but there isn't. The vast VAST majority of the demand for hardware without cameras comes from the NatSec type people, and they're all doing bulk orders so they get more leverage to have niche production runs done for them. And even then they don't always get devices without the cameras. They end up having to do awkward things like physically disabling the hardware after the fact or locking out the functionality with custom firmware.

Before laptop makers started adding them en masse, there very much was an appreciable market for camera-less machines.

I find that pretty far fetched. I'd need to see some actual data on that that isn't explained by the commodity parts getting cheaper to be convinced.

Because before laptops included cameras we used to buy Logitech USB cameras to attach to our laptops.

I still have mine, and sadly it only produces 640x480 images, and everything looks too dark compared to the camera that is now included in the laptop.