[ac29]

BSD style licences dont require source code changes to be released. For example, the PS4 OS is based in part on FreeBSD, which is distributed as binaries. Sony is under no obligation to release any source code changes or contribute anything upstream. Copyright holders for people who wrote FreeBSD code have no legal standing to sue for access to these changes either (I think, but I am not a lawyer).

By contrast Android devices all run the Linux Kernel, which is licenced under the GPLv2. Android device makers are obligated to release the kernel code they use, so users or upstream developers could use it. It's a bit more complicated than that, because the code doesnt necessarily have to be able to be loaded on the device (GPLv2 doesn't say anything about locked bootloaders or cryptographic signing, for example, and binary blobs that work in tandem with GPL code are a bit of a grey area, as far as I know).

Parent commenter prefers the latter style, or possibly even GPLv3, which imposes additional restrictions on what you can do. See Tivoization [0].

[0]https://en.wikipedia.org/wiki/Tivoization