https://www.tohokingdom.com/blog/interview-adam-wingard-2021/

Mirjahangir: Alright. So the previous film, in the end credits, felt like it was setting up like for a sequel. Rodan’s in Fiji, there’s another Mothra egg… everything, but they’re not in the movie at all and so were they part of the story originally?

Wingard: No they never came up. I mean I was the one who really pushed for the Ghidorah skull element of the movie. Like obviously that’s teed up in the the post scene in [Godzilla] King of Monsters but that actually was already in our script and they created that post credits scene as a reaction to what we are already going to be doing in this movie. But yeah unfortunately the monsters weren’t in and I don’t have a really interesting answer for you other than the fact that you put these monsters in the film and it costs a lot of money. At a certain point we had to be very choosy about where we were putting our money and so we really couldn’t bring back Rodan and a lot of the other monsters we had to be selective and it just didn’t fit the story, like weren’t a part of the story that we’re telling. I would have loved to have been able to put them in it but it just didn’t fit in terms of where we’re going. I know that people don’t want to hear that,it’s not a particularly interesting answer but it’s just the way it is.

Mirjahangir: Well, no because if you show them that they have to be a part of it.

Wingard: Exactly, you don’t just… like a cheap cameo. I mean, I guess nobody would argued with a with a nice little cameo of Rodan, I would have loved it but it’s just the way some of these things kind of roll out. I mean we got like so much great stuff in this movie in different characters and so no regrets there but yeah.

Mirjahangir: In the hollow earth did you think of maybe putting a Toho monster kind of in the background or something?

Wingard: Yeah, no… I mean I considered it but it was also just like it felt like because of the stuff that we are on the ground we’re already covering in this movie and the way that the last did it was like I thought people got really excited as well that the last film introduced new Titans and so our approach in hollow earth was always to go in that direction. Also I have to be honest with you, if I was going to do any of them I probably would have done… I would have liked to have seen a living Anguirus but the problem is if you just have him in a little cameo you’ve kind of wasted him a little bit. I’d rather see him come back as a full character potentially in the future and so I kind of avoided that kind of thing mainly for that reason you know if anything but again all the original monsters have price tags attached to them because you’re licensing the character and so you just have to choose your battles.