We considered using a BSD kernel very early on (in the early days of the startup), but pretty quickly decided that the very strong industry support (particularly from ARM SoC vendors) around the Linux kernel made it a more logical choice. License was not a major factor in this decision.
The GPL does create a compliance burden for OEMs (compared to Apache2, BSD, or MIT licenses) and OEMs certainly seem to have a lot of difficulty with this burden, based on complaints I've seen about their handling of license compliance for both Android and non-Android systems. That's a simple fact.
The kernel's "bright line" exception of userspace code making syscalls from being part of it for license compliance purposes is quite helpful in justifying the use of a GPL'd kernel to OEMs and silicon vendors that have severe concerns about GPL "tainting" (be they real or imagined).