Even though seat blocking/capacity limits are supposed to end on May 1st, the seatmap kinda suggests they may still be doing it on this flight as there are only 2 2x seat sections left open. Then again, flights on other days look mostly full, so probably not. Highly unlikely they are doing it because they are planning on subbing a 75S on this route. It could just be there are some FC tickets sold without assigned seats yet. DL625 on 5/9 has 7 seats showing open right now and yet is also J2. So there seem to be other random instances similar to this.