Uncanny Valley
TV pictures are good enough. Anything that requires greater resolution needs to be watched on a PC with zoom/ff/rewind etc.
I'm not sure what advantage is to be gained from watching cartoons in 4K but if you are spending your time noticing the address on the letter on the mantelpiece then its time we spend 1/10th of what is spent on TV research on script writing and country based canned laughter timing.
But, when we see what people are happy to watch on phones and tablets, and more importantly what they are watching, I'd say that for 90% of viewers TV's are 'Job Done'.