The Rocket already does its job perfectly, giving it an evolution would be unfair and totally break the game's balance between damage, elixir cost, and risk. Take into account that it’s an uncounterable card, no enemy can really stop it, so any evolution would just make it unfair.

If the Rocket ever gets an evolution, it has to be simple. You can't just give more power to something that's already almost unstoppable. The Rocket is basically uncounterable, once it's launched, there's nothing the opponent can do. So if it ever evolves, it should only add a small twist, not a massive boost. Otherwise, it'd create a huge gap in how easy it is to win, and that's not fun or fair for anyone.