IMO: Trade war
Courts in China are not independent, let's be honest. Hurting Apple, the crown jewel, is a warning to USA (even if Qualcomm is US based)
Edit: also see Huawei CFO getting jailed etc etc. https://www.bloomberg.com/news/articles/2018-12-05/huawei-cf... China answered....with hundreds of billions in market cap for Apple.