I've also heard (not sure if true or not) that General Consumer Electronics got a really good deal on the 9in vector displays for the first batch run which made production a lot less economically viable later.
https://www.gamedeveloper.com/design/a-history-of-gaming-pla...
> The system got its start in late 1980, when one of the hardware designers at Western Technologies (Smith Engineering), John Ross, had a light bulb go off -- or, to be more precise, a surplus one-inch Cathode Ray Tube (CRT).
> Western Technologies redesigned the system as a tabletop, and later that year General Consumer Electronics (GCE) licensed it for production -- though now with a nine-inch screen.
More of that history here https://www.vectrex.be/vectrex_jay_smith.html