If the radio station has a policy of no dead air or “forward progression” the intro (or talkup) to the vocal may be the only time the DJ is allowed to talk.
Several years ago Mike Joseph programmed a station in Connecticut where the jocks only talked over the end of the song. Allowing seconds to slip by without talking were labeled “missed opportunities.”
That said, there are some jocks who think it’s a personal challenge to talk a record all the way up to the vocal. Years ago I would want to strangle such a jock every time he (they were mostly he’s) talked up Richie Haven’s “Here Comes The Sun.”