I feel like I remember them being cancelled due to a lack of preorders.
And with the lineup of that final boxset I’m not surprised. Burning Godzilla without Destoroyah is weird, the design of that Rodan was a little off and he’s not exactly a big enough gun for people to lose their minds over finally getting him (despite the fan outcry on this particular board), the Mothras were kinda just lil statues but were also the best part of the set, and Megalon came from the... like... second worst Showa Godzilla movie.
It wasn’t what I call an attention getting set. Hell I still don’t have it myself. I regret not getting it for sure, but at the time knowing that this was it for Godzilla it was a bit demotivating to end a line having Megalon and Titanosaurus and not having Ghidorah or, assuming they were venturing into Heisei with set 3, Destoroyah and Biollante.