Also finding a piece of solid metal at the bottom of a pit isn’t exactly comparable to growing a new head.
But finding something that was flow into the gas giant and disintegrated is.
Why do you keep insisting that it fell into the gas giant? There’s so many other things that could have logically happened to it (despite the fact that SW was never too concerned with “logic”). Just because Luke got sucked into a tube that eventually dumped him onto an antenna (a very bizarre thing that only happened for plot reasons I might add) doesn’t mean that that exact thing would’ve happened to the saber.
Even if you have to be picky, there’s so many possible outcomes here.