People can have various reasons for such look. It can be a symbol of non-conformity.

Official Rust spaces have a code of conduct that is inclusive and forbids discrimination, and this may attract people who otherwise wouldn’t feel comfortable to participate.

Because it works everywhere, because it’s so old.

The next best option, a decade old WebP, is a mixed bag. In its best-compressing mode it will lower color resolution and add fringing like a JPEG. In its lossless mode it may be bigger than GIF.

If you have an option to use a proper video format, go for it. But often sites just allow upload of GIFs. If you send a newsletter you never know how primitive (Outlook) the client will be.