Well, yeah, by "they" I meant some pharma PR division or the CDC or someone.

I could come up with some explanation, like "Jab at least describes an injection while dose is a broader term, so they go with 'jab' because they find too many people would reject 'dose' as inaccurate and fall back to 'injection', which they are trying to avoid", but I am happily not a PR focus group guy, so I don't know. But when an unusual word suddenly starts being used by everybody to describe some politically charged thing everyone used to use a different word for, I think it's safe to assume some PR opinion-manipulation is behind it all.