Fiber is generally laid just once. But the filament is a recurring cost to consumers so it provides more value to businesses ... and therefore more opportunity for a higher demand and higher price.
Does seem very much that the whole 3D filement market just needs one disruptive supplier. Which often happens when you have high-margin consumables markets. Which with the ink printer market saw makes of the printers introduce DRM into the consumables - something I don't see happing with 3D filement though, so could be interesting.
That all said, I see that there are products that can convert your plastic bottles into 3D printer filement - https://3devo.wpmudev.host/filament-makers/