Because they literally operated it as a honeypot and gave police full access to chats while advertising to criminals that it was safe.
EncroChat first came to the attention of the media when it was revealed that high-profile criminals Mark Fellows and Steven Boyle had been using the encrypted devices to communicate during the May 2018 gangland murder of John Kinsella in Rainhill, England.[16][9][17] The service resurfaced in the media during the summer of 2020 after law enforcement agencies announced that they had infiltrated the encrypted network and investigative journalist Joseph Cox, who had been reviewing EncroChat for months, published an exposé in Vice Motherboard