Are those cheap? Not being sarcastic. I honestly don't know if they're selling those at a loss. I bought my Sony Smart TV 4 years ago. I don't get any ads. It's got some apps like Youtube, Netflix, Stan etc. and that's it. No ads whatsoever.
Probably 4 years ago was when they made money just by collecting telemetry on TV usage.
Also, 4 years ago was roughly when Windows 10 became widespread surpassing Windows 7, and forced many users to adapt to advertising in non-phone products, therefore manufacturers may have interpreted this as less resistance to ads.