Symbolic Software's Nadim Kobeissi told The Verge that it likely took a while for the Chinese government to figure out how to configure its infamous firewall to detect and block the heavily encrypted protocol WhatsApp uses to send text messages. Since the country's efforts paid off, that could mean that it now has the capability to take on similarly secure protocols.
WhatsApp's end-to-end encryption was probably the reason why China targeted it in the first place. While the country is known for having rigid internet censorship, it's been ramping up its efforts even more in preparation for the 19th Communist Party congress this fall, where the government is slated to choose its new leaders. By preventing its citizens from using secure applications like WhatsApp, China is likely hoping to force them to use alternatives it can easily monitor. WeChat, for instance, provides the Chinese government with its users' personal data.
Facebook declined to talk to The New York Times about the situation, but it was definitely a setback for the social network. The company's main website and app are blocked in China, and WhatsApp was one of its last properties that still worked in a massive market with a billion potential users.