Overall, the rise of domestically-made Android phones are probably the biggest reason of their demise. But if we have to point at one specific instance, arguably it’s the Note 7 debacle. Samsung completely mishandled the situation - they refused to recall the devices in China despite doing so in other countries, and when some customers posted pictures of their burned phone, Samsung threatened them. And of course consumers voted with their wallet, and nowadays it’s rare to see Samsung phones in China.