Why does GIMP change the BPP ?

[Mark2855]

Thanks for your reply, Rich.
No, I'm not sure of the terminology.
Irfanview says that each of the pictures IS 1920 x 1200 pixels, 24 BPP, about 300KB each.
Yes, Gimp > Image > Precision shows "8 bit integer" as well as "perceptual gamma (sRGB). I don't know what that means.
Not Grayscale... full color.
The output GIF file is 7.4MB.
I've never before heard of .WEBP file. Just looked it up.
Found some sample files. They simply look like Pictures.
Can a WEBP file do animated stuff, like a GIF?
What else can I tell you, to explain the problem?
Thanks.