Unfortunately I think computer books in general are on the decline. It's just very hard for that medium to keep up with the pace of change. This saddens me because it is by far my preferred method of learning new technology, but it certainly seems like video content is winning out over books. YouTube, Udemy, WWDC videos, and similar seem to be the best way to get up to date information now.
There are still some high quality publishers out there, but I fear that we're coming to the end of an era. In addition to the ones you mentioned Manning and No Starch Press produce consistently excellent books as well.
I‘m not sure if it’s really the pace of change or if many people just cannot focus on something for more than 10 or 15 minutes anymore. I‘m aware many people learn from YouTube videos and short tutorials, but I often find what they is quite shallow.
There are still some high quality publishers out there, but I fear that we're coming to the end of an era. In addition to the ones you mentioned Manning and No Starch Press produce consistently excellent books as well.