>How do you think manufactures can afford to sell these large screens at such cheap prices.
TV prices have been falling for decades[1], long before manufacturers could truly benefit from the data provided by smart TVs. So other factors are probably much more important - such as cheaper materials, automated production, economies of scale etc.
Also, ad revenue wouldn't explain why "stupid" computer monitor prices have also fallen greatly during the same time period.
[1] https://u.osu.edu/zagorsky.1/2014/05/18/why-are-television-s...