The issue is not that they believe /dev/urandom to be bad, but that it flat out isn't guaranteed to be available: If you're chroot'ed, chances are you won't have read access (or see) /dev/urandom. Furthermore, if you've run out of file handles (maybe intentionally - because someone figures they can try to DOS you to attack the PRNG), it is not a given you'll be able to open it even if it's visible.
LibreSSL tries /dev/urandom first, then falls back on a deprecated sysctl() interface, then tries it's own "last resort fallback".
Then abort if it's not available? A lot of software (most?) doesn't work with an empty /dev. At least null is othen required, so why not throw urandom in there as well?
The source explains why the developers does not see aborting as acceptable: It opens a huge security hole on systems where core files are insufficiently secured. On systems that are properly secured, it's a single define to cause it to fail hard when it can't use either /dev/urandom or sysctl().
LibreSSL tries /dev/urandom first, then falls back on a deprecated sysctl() interface, then tries it's own "last resort fallback".