The problem with backmasking is the mind tends to seek out something familiar and make sense of things. If it hears gibberish it will search out something that sounds familiar, but that requires it to fill in the blanks.There's a video on YT called 'Paul McCartney is Dead - songs backwards' and during one of the clips played backwards you can def hear 'Paul is a dead man, Paul is a dead man'. They prob did it bc they could and I hope it wasn't done for bad reasons. Just caused a lot of kerfuffle at the time over what it meant, at least to some Beatlemaniacs.
Also most of the time people are aware of what they're "supposed to hear" and are actively seeking it out. That puts expectation and bias in making it easier to "hear" things.