The same reason Audacy chose WINS as the station to consolidate their all-news operation, and to simulcast on FM. Audacy's purchase agreement from CBS included the sole rights to the WINS call letters (which, by law, can't be owned by CBS without one of their remaining TV stations holding them). Obviously, CBS holds the rights to the WCBS calls, by virtue of their TV station, but allows Audacy to "borrow" them under whatever circumstances are agreed upon (ones that apparently are vague to the public). Similar agreements are present in many markets where long-established radio stations have been sold by a company while retaining the TV station with the same calls. Hope that explanation makes some sort of sense.