Because most of us just run with whatever Apple rolls out. We'll embrace and gush about iPhones being able to shoot 4K but put down 4K when talking about the new

TV because Apple left it out of that product (for now). It's like we're split personality PR agents.
Apple usually makes it easy by taking a full stance one way or another. But sometimes they will embrace and not embrace at the same time in new product announcements. This was one of those. Apple once rolled out a retina iPad and a non-retina iPad Mini in the same presentation. Many of us argued why the retina iPad was a "must have" upgrade AND argued why the mini didn't need retina... until the next year when the next mini went retina. Then, it too was a must-have upgrade.
Same here. 4K in an

TV will be a gimmick, "no one can see the difference", "until the whole internet is upgraded", file sizes, seating distances, and so on will be spun and spun and spun... until Apple rolls out an

TV with 4K and then it will be "shut up and take my money". This was exactly how it was when Apple clung to 720p in

TV while pretty much everything else had gone 1080p (including iDevices recording resolution).
I think this

TV is great. The app store alone makes it a fantastic product. But I wish they would have gone ahead and gone 4K here too... just for those that want 4K now (the rest of us could continue to watch our definition of "good enough" even if we never downloaded a 4K video). If nothing else, shortly there will be tens of millions of new iPhone owners looking for a way to actually play the 4K they shoot on their new phones on a 4K screen.
Based on the past, what will happen next is iPads will go 4K (recording) probably next year and either at the same time or soon after Apple will roll out an

TV5. All these people arguing so hard against the merits of 4K won't rant against Apple once Apple goes there. Apparently, it's only a gimmick, stupid, "no one can see the difference" right up until Apple rolls out a product with it.