Why did Godzilla's roar change after 1991?

I dont know man maybe he evoled maybe when he fell in the lava he evoled cuz he had a diffrent look after 84 

Personally, I enjoyed all the changes to his roar throughout the years. Though I have agree, 84' had one hell of a roar. Would love to have that mixed with the Millenium version. <3

I think the change came about because of the shift in tone. 84 and 89 were on the grittier side, but when it started to become lighter and more fantastical, it changed to a higher pitch for the sake of being more audience friendly.

Like to hear GMAN's take haha

I honestly have no idea. Wolfguy's reasoning seems plausable, but it's something I've often wondered about myself. I'm not sure what prompted Toho to change it.

It's something I've wondered about for years too.  The only thing I can think of is once they changed the roar what they changed it to sounded more like the roar of every Godzilla prior to Godzilla 1984 (except for the original's roar being slightly different) so many they changed it to get back to Godzilla's basics/routes?

I agree though the 84 roar sounded brutal/mean... like I would not want to be anywhere near that thing!

I agree with Hazzardkitsune, I also enjoy the different roars.

I still think they should have kept it

Its possible that the roar changed due to the advances in technology my favorite roar is the burning godzilla and the 84 roars respectively.

I've always loved Godzilla's lower pitched roar. Why they changed it in "Godzilla vs Mothra" I don't know, and I really don't have any problems with it. But I think they did it because Toho wanted to attract a younger audience, and not scare them with a roar that sounds like it came out of a monster from hell.