On the other side of things - why should you assume that this other box, which you can only get from a super sketchy online dealer and which gives you something for nothing that you're accustomed to having to pay for, is legit?
Because "is legit" is the default for stuff you buy out in the open. People naturally (and mostly correctly) assume that if you don't have to know a guy who knows a guy and you're not paying in unmarked bills with nonsequential serial numbers, it's legitimate.
Keep in mind that recognizing an online seller as "sketchy" requires a great deal of technical skill all by itself. To the average Joe, there's not much difference between eBay and Amazon. Hell, I just searched for "kodi" on Amazon and turned up a ton of stuff there advertising free movies and TV shows. Amazon! You want to tell me that the average person should see something sold on Amazon with Prime shipping that says you can use it to stream movies and TV for free, and understand that this is not legal?
It's even worse than that. There's literally signs on my street now advertising for a local company that sells Android sticks with Kodi preloaded and a bunch of piracy channels.
Are normal people supposed to expect companies that advertise out in the open like that to not be legitimate? And I mean... they sort of are, they can deliver what they're advertising, they'll come to your house and set it all up and even give you support. Most consumers wouldn't know (or likely even care much about) the difference.
Wow. I had the idea this was mostly a thing you'd find in the sketchier corners of eBay, and that at least to some extent you'd have to go looking for. But that's not so, which rather cuts my argument off at the knees.
I thought the same thing initially. I started writing something about Amazon Marketplace sellers, then had a "wait a minute..." thought and tried searching for "kodi." I was quite surprised!