I couldn’t quickly find a link to a site without ad cancer, but there are many stories of the WhatsApp creator calling out FB for destroying the app:

Reporter Elizabeth Dwoskin claims that the move came as a result of Koum’s disagreements with “Facebook’s attempts to use [WhatsApp]'s personal data and weaken its encryption.” The report describes how those issues gradually emerged after Facebook’s purchase of the encrypted-messaging platform for $16 billion in 2014 and how they led Koum to inform Facebook’s corporate leadership of his impending departure. From the sound of things, these disagreements began taking shape well before the company’s Cambridge Analytica scandal.