If by "people" you mean me, I'll tell you why: I'd like Apple to lead with this. I like my

TVs very much but it's easy to see where they can improve. Rather than settle for the now or even "old technology", I'd like to see them push the envelope here. It's not about disliking Apple, it's about wanting them to deliver something
ahead of the curve... you know, like they do with iPhones, iPads, Macs, Watches and so on.
In this case and IMO, 4K is close enough to go ahead and embrace it. Those thrilled with 1080p can still enjoy their 1080p to the MAX with hardware capable of more than 1080p. But it doesn't work the other way.
More simply, if "people" like you are completely satisfied with 1080p (or 720p) as your max, a 4K

TV would have NO EFFECT on you- you could still consume 1080p (or 720p) to your hearts content on such a box. In fact, a 4K

TV would probably drive down prices of 1080p

TV boxes so you could probably save money too.
However, other people (who are not you) craving 4K playback options for their 4K TVs could get what they want from a little Apple box too. You get your 1080p (or 720p) and they get their 4K. Everybody wins. Cling to a 1080p MAX and a segment of buyers can't get what they want from Apple (for now) so they buy someone else's products.