All aircraft have some seats blocks for those who are disabled or need assistance. I think some also have blocked seats for UAM's. This isn't limited to CR2's.
This is at least somewhat new for the CR2s. My last itinerary on DL with CR2 flights was just over a year ago and at the time I had no problem getting 1B/C on both flights and rarely had a problem getting it on flights before that. It was always a Blue "Preferred" seat but all seats in Row 1 were available for selection.