TL;DR: LinkedIn makes it really easy for Chinese spy agencies to identify suitable targets at companies or government orgs of interest and contact them innocuously in the form of recruiters. While this much is by design, a LinkedIn profile also often has enough information to let them deduce that a person's career is not going well or they're in financial trouble, making them particularly susceptible to bribery or blackmail:

> For example, Kevin Mallory, a former CIA officer, was sentenced to 20 years in prison for handing over secret documents and confidential information to Chinese intelligence. His career was floundering and he was in dire financial straits when he received a message from a fake account on LinkedIn in 2017. This fake contact claimed to be working for a think tank that was looking for foreign policy expertise. The targeted ex-CIA officer travelled to China twice and was given money and equipment to maintain his communications with the Chinese.

One point not raised by the article is that two can play at this game: LinkedIn is allowed to operate in China and has some 41 million users, and there's a local unicorn called Maimai (脉脉) that's increasingly popular as well.