You'll see big differences in 4K with very large screens like Billboard sized or in Movies (which are 2k atm).
But then again very few people wanna invest in a +50 inch TV (where until +80 its still a small difference).
Hell I think my 42 inch TV is big enough, any bigger and I couldn't move by myself and it wouldn't fit in my small car.
And then there's price, the cheapest 4K TV I've ever seen was $700 but that was only 39 inch, $1500 for 50 inch, then it jumps to $5k for 55-58 inch.