There are companies doing that, the 3D printers are however highly specialized and expensive.
It's surprisingly easy to 3D print the shape of a lens and polish by hand. I made a working telescope this way with a 3D-printed body and two cast epoxy lenses. As an added bonus, you can easily make aspherical lenses this way.
If you coat the surface with silver you can also make mirrors, but the polishing requirements for this are a lot more difficult. My attempts at a 3D-printed telescope mirror have very bad image quality compared to the excellent results from the lenses.
Would be a much interesting article than the one at the link (not your link, the original HN clickbaity link)