I.e., people don't intuitively understand what "good" or "useful" is—those terms are mired in tons of prescriptive statements made by ideologues that get you confused. But "awesome" (or in this case, "joyous") isn't really a property people ever insist that something has for political reasons. It's something you've probably only ever heard as a descriptive word referring to things that are genuinely "awesome"/"joyous", and so your intuition on what is "awesome"/"joyous" is likely much more solid and easier to "hear."
I would also argue that "joy" is a pretty useful word in the sense that asking about a thing's utility conjures images of sterile pro/con lists of a thing's immediate usefulness right now; while "joy" might be an acute nostalgia, or the sense of determined hypomania brought on by a clearly-imagined-and-still-enthusiastic plan of what you will be doing with the thing a year from now.
That's an interesting take and maybe that's what she's doing. Plus, I think she is making this idea accessible to people by putting it in very simple terms -despite my misgivings.
Interestingly, another commenter mentioned that the actual word in Japanese isn't joy or sparking joy, but rather heart throb [https://news.ycombinator.com/item?id=18865829] which to me would eliminate quite a few more useful things that aren't as emotion inducing.
All this reminds me of someone I worked with who said she liked Kondo's advice and took it to throw out anything she hadn't worn in six months. Which seemed like a wasteful way of thinking. [i.e. don't like something now nor for the past six months, toss; then month later, aha, I need that thing, lemme buy a new one. And what about Winter clothes or Summer clothes, etc.]
I.e., people don't intuitively understand what "good" or "useful" is—those terms are mired in tons of prescriptive statements made by ideologues that get you confused. But "awesome" (or in this case, "joyous") isn't really a property people ever insist that something has for political reasons. It's something you've probably only ever heard as a descriptive word referring to things that are genuinely "awesome"/"joyous", and so your intuition on what is "awesome"/"joyous" is likely much more solid and easier to "hear."
I would also argue that "joy" is a pretty useful word in the sense that asking about a thing's utility conjures images of sterile pro/con lists of a thing's immediate usefulness right now; while "joy" might be an acute nostalgia, or the sense of determined hypomania brought on by a clearly-imagined-and-still-enthusiastic plan of what you will be doing with the thing a year from now.