Oh, this is a very, very simple answer.
Regardless of what the TV manufacturers wish you would believe, 4K is a gimmick for every environment except a large commercial theater. It is a way to try and sell consumers another piece of electronic equipment with exciting specifications that has no benefit.
Given the eye's resolving power and the average distance people sit from a TV, you need a bare minimum of 120" screen size to even physically see any difference at all - and even in that case, the difference is minute that would rarely be detected. In reality, 4k is only useful for large commercial theaters which have screen sizes many times that size.
So, going back to your answer, why does an under $2000 APS-C professional camera not have 4k? Well, most likely because if someone is filming something for a large commercial theater they are going to use something a bit better than a $2000 APS-C DSLR; if the filmmaker does use an APS-C DSLR because quality is not a priority, then obviously 4k doesn't matter either. So, Canon is simply focusing on putting out a product with features that will actually be used by professionals in this price bracket, i.e. sports and birding. 4K would go unused by a professional in this type of camera.
And, why do smartphones and Panasonics have 4k? Because it is a gimmick feature they can try to lure consumers to their product with, even if it has no benefit to that consumer in any application they could possibly use it in - except possibly that Panasonic could further profit by selling you a 4K tv so you can display your videos in native 4K (that in reality looks no better than 1080p even in a home theater). Still, with some juicy marketing the consumer will think they have the next best thing and revel that they did their research to get the latest and greatest technology; they will think that they got this great new feature even the expensive 7D2 does not have! Unfortunately for that consumer, they were duped.
You think professionals who capture in 4k always intend to deliver in 4k?
Aren't you aware of the framing abilities 4k offers if you deliver in 1080p?
Aren't you aware of the sharpness, noise, and color space benefits of downsampling 4k to 1080p?
You think professionals would not use 4k if it were in the 7d2?
You think professionals didn't use the 5d and 7d?
You think professionals aren't using the GH4?
You think professionals aren't using the A7s?
You think professionals aren't using the Black Magic 4K Camera?But most of all, you think professionals don't want something from Canon that can compete with the performance of the above cameras at a similar price-point?!?!
Maybe you think the only video "professionals" are those working in Hollywood on giant blockbusters. Just as the only "professional" photogs are those shooting for NatGeo and Sports Illustrated, right?