Supply and demand. Unfortunately there are way more people that would rather the lower price than the ad-free.
- Imperfect information, aka Market for Lemons: It can be hard to find out how prevalent ads will be when buying a product. Consumers often make a purchasing decision without knowledge about ads.
- Changing terms after lock-in, aka Enshittification: Manufacturers (like Hisense here) can add advertising to products after consumers have already bought them. Initially, consumers have negotiation power since they can freely choose a product, but later they are locked in and cannot easily react to the manufacturer changing the product to their detriment.