OP, if Amazon and Roku can ship 4K-playback boxes that cost a lot less than
TV, licensing cost was not an obstacle.
The lack of 4K content for

TV in the iTunes store is not the reason either. Why? It makes no sense at all to put 4K content for

TV in the iTunes store until there are lots of 4K

TV boxes in homes to play it.
The hardware must come first- or at least at the same time- else, not $1 could be made if EVERYTHING in the iTunes store had a 4K video option for

TV right now. It would be the same with loading up stores with 4K blu ray discs right now. How can any of those discs sell before there are 4K players also for sale and in which to play those discs?
The perception of the lack of much 4K video is lame. Lack of 4K content is almost entirely driven by lack of a mainstream channel through which to deliver 4K content. As soon as there is a way to monetize 4K with the masses, 4K content availability will explode. Apple could have led the way there but chose to cling to 1080p instead. This excuse of lack of much 4K content availability seems to justify that decision but lack of broad software support of 3D touch or Apple Pay or TouchID or FaceTime or most relevantly- AppleTV apps for sale- didn't hold Apple back from rolling out new hardware capable of such features and leaving it to the software producers to play catch up with that new hardware.
Pretty much every film ever shot- movies & TV- is already stored at greater than 4K content. Monetizing it in 4K only awaits a mainstream channel to make it (profitably) worth rolling it all out in 4K. Apple could have led that charge instead of probably moving on 4K last... exactly as they did with 1080p. It is a good move for shareholders as they get to sell lots of us the 4 now and the 5 "now with 4K" later, just as they sold us the 2 and then the 3 "now with 1080p" a few years ago.
Will simplifying the licensing processes & costs help? Sure. Was it the reason Apple didn't roll this out with 4K? Only Apple could say for sure but I suggest almost certainly not per the above. Again, if much cheaper boxes from Amazon & Roku can embrace 4K, licensing costs was probably NOT the issue.