Remember how whatsapp for years didn't let you delete sent messages even if the other person hadn't yet received it? I assume there was some major privacy reaso

Remember how whatsapp for years didn't let you delete sent messages even if the other person hadn't yet received it? I assume there was some major privacy reason why it worked that way for so long because it was obviously pretty horrible from a user experience standpoint. Would anyone be able to explain it to me? And what kind of extra data did facebook likely receive from adding that feature (which I think coincided with when the creators started to get very unsettled at Facebook).