The internet's attack surface is infinite
Hundreds of millions of domains are registered every year and of these, a huge amount are spun up with malicious intent. To monitor and scan such vast volumes for fraudulent activity, powerful technology is required. However, most domain discovery and security offerings aren’t capable of scanning and analyzing at such a large scale.
In addition, the majority of vendors only focus on top-level domains (TLDs) and do not offer subdomain scanning. So, subdomains become an infinite attack surface where bad actors will try to hide their threats.