Doing this doubles costs and certification time for the console patches and it’s very likely blizzard isn’t willing to spend more money and run through the process twice instead of mushing them together to save cycle time and console certification of their patches?
If they owned the consoles it’d be different, but this is basically through 3 other large companies software distribution systems who will NOT just passthrough downloads to their users machines. It needs to run through their verification process first and that’s also probably not free.
Also if you’re thinking of releasing all the data at once they also likely have concerns about datamining. While there are a lot of people who don’t care about how “surprising” the skins are, or other leaks… Blizzard seems to care a lot and does their damndest not to have information released early.