Can We dub the original?

Speak for yourself. I can't stand dubbed versions and I love watching Godzilla movies in Japanese with subtitles. It elevates the experience for me.

As for the reason the original hasn't been dubbed-- The 1954 film has sorta been looked at by distributors as something too good to be dubbed. Railto, Classic Media and Criterion treat it like an art film (whether people agree it is or not) and don't want to lower the calibar of the movie by creating a tacky dubbed track for it.

I for one don't mind this. I'd never watch the original version dubbed.

I'm not sure why it hasn't. The Japanese dubbed King of the Monsters.

Subs over dubs any day of the week and twice on Sunday for me, man!  I've always wondered why dubbing the original version has never happened, but I'm fine that it hasn't.  Seeing the Japanese version with subtitles was a revelation to me when I first watched it, and I've only watched King of Monsters a few times since.  I spent years locating the subtitled versions of all the films, and enjoy alternating between the American and Japanese versions.  While the dubs will always be nastalgic, when I want to experience the films the way they were meant to be seen, I watch the subtitled versions.  I think dubbing Gojira would be like dubbing Seven Samurai... it would just be insulting to the original.  No one would watch dubbed Kurosawa, nor should they.

The same reason they haven't redubbed Godzilla raids again to make it actually refer to him as Godzilla and not use Aguirus's roar.

Lazyness

^Not really laziness, there's just no market interest. Dubbing Raids Again and the original movie would still cost a good deal of money. No reason to do that when subbing them is cheaper and there's more of a market for it these days.

the original japanese masterpiece must not be dubbed

I personally want to see every Godzilla movie in there original cuts and in their original language.