In a vacuum, sure, this isn't a big deal. Most people buying into an Apple TV probably already have at least one USB-C cable-- and if not, they're easily obtainable and cheap.
That said, my two gripes with this are:
1) When pressed, they will say this is for the environment. How does it help the environment for me to have Amazon ship me a USB-C cable vs. one being included in the box? At any rate, it's very clearly not about the environment as much as the bottom line, so this comes off as insulting.
2) Regardless of the environmental question, it is undeniably a better user experience to receive everything you need to use a product in the box. How stoked are you when something like a smoke detector comes with an Energizer in the box? The fact that they are willing to sacrifice that improved user experience over a cable or two that cost them pennies to include in the box speaks a lot about the mindset of the company's leaders.
So, while this instance itself is a relatively small issue, it's indicative of a larger trend towards a preachy, dishonest, bean-counting Apple where shaving pennies off of production costs is worth it even if it means a somewhat diminished user experience. And they think you're dumb enough to believe that it's for the environment.