Every time a company like Microsoft or Facebook talks about how my messages are E2EE inside of their app I always read: "Now only we and you can read your messa

Every time a company like Microsoft or Facebook talks about how my messages are E2EE inside of their app I always read: "Now only we and you can read your messages, no one else." What's the point of E2EE if you can't be sure that the decrypting app isn't sending your data elsewhere?