Clarity regarding version 1.1 changes

While going through the docs for v1.1, i had a minor doubt regarding the version in JSON:API Object.
why is the version included here instead of in the accept header or content-typ header. something like application/vnd.api+json:v1.1 or something similar?

I think the answer is that new versions are promised to be always backwards compatible.

https://jsonapi.org/format/#status