You have. It's your server and it's your wrong / terrible configuration.
I have an own subdomain service - customer name -> customer subdomain. There is a wildcard certificate, every customer subdomain is added manually (to the dns).
Some customers add own cname entries:
special-name.main-domain-of-the-customer.com -> CNAME server-daten.de
But I have to add a relation
special-name.main-domain-of-the-customer.com -> Goto that customer database + subfolder
So no random domain name works via connecting the ip and sending a domain name or a server-daten.de subdomain as hostname. And no certificate is created.
A wildcard dns entry + a wildcard webserver is a critical configuration. Because it's too open.
Failed validations have their own limit, that's not the 50 / week limit.