I always assumed that was the reason too, but it feels like there was really only a narrow window when there was a significant crossover between monitor panels

I always assumed that was the reason too, but it feels like there was really only a narrow window when there was a significant crossover between monitor panels and TV panels. Most all new TVs are 32" or larger, so that's not going to widely impact what 20-27" monitor panels can benefit from. Even when smaller LCD TVs were popular, they were often 720p or 1266x768 panels, but most monitors were 1080p. OTOH, maybe it was more of a second-order thing: people were primed from TV and movies to expect wide-format content, so monitor makers had to produce products that satisfied that; people don't like letterboxed/pillarboxed displays.