Well, the database might be large. Millions of domain names, each with like a dozen (or more) records. (maybe 1k * 30 million domains).

But mostly it's about how the DNS changes, a lot. Sites move, geo records, etc. Getting those changes to every household would be a lot of traffic.

Before DNS folk were sharing a common /etc/hosts file - and quickly determined there had to be a better way.

So, DNS with a dozen root servers that stay fresh, caching down stream.