TV's were expected in that time period to last 20+ years, they were a major investment.
The other interesting thing about Zenith is, its not uncommon to buy an older Zenith table top radio and have it work out of the box (and by older, I mean, tubes), they use mostly Mica Capacitors, and they seem to last forever.
https://spectrum.ieee.org/zenith-tv
Delves deeper into the "lower cost of overseas manfuacturing" as cause of death for the US TV industry, with a focus on Zenith. Zenith saw this coming and tried to avoid it by investing in technology and R&D - and unfortunately chose to invest in technically superior but unpopular or uncommoditizable technologies like Betamax, digital signal transmission standards, and early analog HDTV. Heck, they paid to develop the standard for stereo TV broadcast audio, then gave it away royalty-free.
Interestingly enough, there is still a small rump of Zenith humming along in Illinois, mostly doing R&D and Technology Licensing. LG owns them now, I've often wondered if LG ever introduced US Television production, if they'd do it under the Zenith brand name.
Zenith's TV engineering business was bought out by South Korea's LG, and Zenith's role as main guiding force behind North America's ATSC digital TV broadcast system was grandfathered to LG with many of the same people.
Zenith was quite successful, and was making TV sets in the US until the early 90's - but eventually the lower cost of overseas manufacturing caught up with them.
Motorola and Western are the saddest though, Motorola made everything, soup to nuts used in their products, and then bit by bit sold off the bits util they were left with two way radios (Motorola Solutions is the survivor of the original Motorola Inc). Western never really figured out divestiture, there are bits of pieces of it left, if anything Avaya is the closest to a spiritual successor to it (part numbering styles and engineering style).