This is not unlike the CM Main Entrance pass which allows you to entrance to different parks on certain days -- or some days no parks at all. That part is nothing new, but what is new is that they've heavied up on block out dates
significantly in the past 6 months, with no availability to Disneyland park
at all on weekends anymore and only access to DCA on some. It used to be that these types of blockouts only happened during the busiest times of the year, but now it appears to be year-round.
Makes me wonder if they are intentionally playing around with the Main Entrance pass as a way of studying the impact of park-specific blockouts in preparation for doing the same with the APs.
I've posted this here before, but here it is again in anyone is interested! Gives some insight into what they're doing:
https://blockoutdates.disney.com/app/#/