This is the kind of unfounded complaints we've seen from people about Apple going back at least to the 1980s. More recently, there was an "outcry" when Apple waited a few months to release the latest version of OS X as open source after releasing the retail version.
Truth is, Apple is pretty good about open sourcing their stuff, especially when compared to their peers (Microsoft, Oracle). But that doesn't fit the "Google good, Apple bad" narrative that is popular in some circles.
It's important to remember that Android being "open" is googles attempt to commoditize a competitors product... you don't see google open sourcing core technologies related to source.
Truth is, Apple is pretty good about open sourcing their stuff, especially when compared to their peers (Microsoft, Oracle). But that doesn't fit the "Google good, Apple bad" narrative that is popular in some circles.
It's important to remember that Android being "open" is googles attempt to commoditize a competitors product... you don't see google open sourcing core technologies related to source.