I have mixed feelings about this. On paper you're of course right and a copyleft license would be better, but in practice I don't think it matters all that much for something as small as coreutils. It's just yet another implementation of a standardized interface, nobody is going to fork it and build a billion-dollar business around it. Any change or improvement is probably worth more when upstreamed than when kept in a proprietary fork, just because your maintenance burden is lessened.

Besides, we've evolved a bit since the 90s/00s: the main risk to software freedom is no longer binary blobs but cloud services - and the GPL doesn't save you there. And any license requiring disclosing your coreutils to anyone accessing your computer over the internet would be a massive dealbreaker to most people...