I don't think it's that most people can't notice but no one has shown to them what proper TV IQ is supposed to be like or what good headphones are supposed to sound like. A lot of people are convinced that Toyota Camry is a good car, that Beats/Bose sound great, that Nike makes good running shoes and that LED is superior. It has a lot to do with marketing and lack of people's understanding of technology/products that require more extensive research (not your easy PS4 vs. Wii U type of search).
If you read marketing studies, 80% of consumers make purchases based on emotions rather than logic. Since LEDs were the popular TV tech and plasma was branded old tech, power inefficient, the marketing won over the mainstream consumer. When my parents were looking to buy a new TV 7 years ago, I told them to be open minded and compare LCD to Plasma. They actually spent their time and on their own without reading reviews found the Pioneer Kuro and Panasonic plasma to be their top 2 picks! 2 years ago they were looking to upgrade and still found high end LEDs lacking.
Most consumers aren't like that. They go with what's advertised as new and cool. CNET and AV forums have for years given top marks to plasmas as the best TVs for movie watching and sports but the average consumer doesn't read professional reviews or goes into detailed comparisons. The other problem is the poor calibration of plasma TVs at places like BestBuy and side-by-side comparisons of overly saturated LEDs. A lot of people like the oversaturated color over more accurate color. Let's not forget that in a brightly lit showroom store, there will be a major reflection on most plasmas and who wants to stare at a TV and see themselves in it like a mirror?
You can see how marketing sells Bose, Beats, etc. It is unfortunate that plasma died but it was going to be too expensive to reliably make 4K plasma screens and again marketing would have won immediately when given the choice between 4K LED and 1080p plasma. My friends who weren't biased and also took their time to compare TVs have all chosen plasma in the last 5 years. Moving forward though it seems 4K LEDs will be a dominant force and it will be an uphill battle for the OLED.