Remember when DNS was created, and that answers your question. It's the same reason why FTP is terrible, and SMTP allows spoofing. The DNS protocol has been u

Remember when DNS was created, and that answers your question. It's the same reason why FTP is terrible, and SMTP allows spoofing. The DNS protocol has been updated with additional record-types over time, but the protocol itself is largely unchanged since the time it was created, when the network was smaller, and the world was more trusting.