"Most GA pilots have a rounded experience."
Quite correct Encore, but most Airline/Long-term AOC pilots don't. They might have had in their dim and distant pasts, but not currently.
That is precisely why the advert mentions this preference (as well as other preferences).
The advert lays down the experience and Licencing requirements for this operation, and it's detail is an attempt to cut down on the inevitable "snowstorm" of CVs from unsuitable (but, without doubt, very able within their own environment) applicants.
Jez