UX is fleeting. Even the best UX will grow stale over time as styles change, and it's style propagates (as it will if it is truly revolutionary) it will become mundane.
Technology breakthroughs are hacks in the laws of physics. Humanity hasn't fundamentally redesigned the Steam Engine since James Watt. It just can't become more efficient. Nobody cares steam is mundane, or well understood. We still use it in nearly ever power plant.
So no I don't stand why people feel the need to own something as fleeting as a singular moment in the pseudo-cultural-artistic space Product/UX design fits in knowing that it'll pass and forever be looked on as an out of style relic of a by-gone age. To do so honestly and earnestly makes you sound like a diva.
One analogy is brute force searching for an approximate solution to an optimization problem.
It's problematic when others take your solution if you did all the brute forcing.
Design is only fleeting inasmuch as an approximation could be fleeting. Others build off an approximation to find better solutions. But without the earlier solution, we'd find ourselves in a much different part of the sample space.
Definitely, could definitely understand if it was about money/business. But that is never mentioned when designers get angry about their designs being stolen.
I think it's not about money/business. I think it's a different mindset where a "stolen" design devalues your own contribution. A developer who makes a breakthrough never feels like their contribution is devalued if someone else copies your idea; quite the opposite, copies validates that you made a genuine breakthrough.
In Xiaomi's case, what they're doing is, more or less, that last bit: the only work they're putting into their designs is the work necessary to make them look like somebody else's designs, expressly because the designs they're copying are successful in the marketplace. If I was a designer they copied I wouldn't be very thrilled by that. Money definitely plays into that, but credit for the design work is a big part, too.
How can you paint such a broad stroke, like THOSE DESIGNERS, I'LL NEVER UNDERSTAND THEM! With the implication being those designers aren't open and collaborative and willing to share and don't understand iterating in the open like us developers. The quote is from one specific designer.