For many viewers Bumblebee is the robot who speaks in snippets of songs and radio broadcasts. But it wasn't always so, and the reasons differ between versions.
In the classics he's chatty
In the 1984 cartoon Bumblebee speaks with a normal voice — and quite a lot. He's cheerful, friendly and the first to bond with humans, especially Spike.
The films: a broken voice box
In the 2007 film Bumblebee can't speak because his voice box is damaged, so he communicates by picking phrases from the radio. Bumblebee (2018) shows how it happened: the Decepticon Blitzwing rips out his voice box during a fight on Earth.
Prime and beyond
In Transformers: Prime Bumblebee has also lost his voice because of Megatron and communicates in beeps and whirs the other Autobots understand. By the end of the story his voice returns, and in Robots in Disguise he is a team leader who speaks for himself.
Why the idea stuck
A mute hero makes the audience read emotions through gesture, eyes and music. That's why Bumblebee became so touching: like a child still learning to speak, and at the same time the most loyal friend.
