As someone with the authority and means to shut down domains for exactly this, the truth is, most people have either used email addresses they never check, or, just ignore all warnings. I'd argue >75% of people contacted never reply. Their entire domain gets shut down, and then, probably 75% of those do finally contact asking why their domain is down. It's probably most likely that since WHOIS data is public, people just don't put addresses they check often there.