[georgyo]

There are too many reasons to list. But the primary reasons DNS is a hierarchy of DNS services hosted by many distinct groups. And DNS records are queriable publicly, but also consider private. Almost all servers in the world disable AFRX for a variety reasons.

Beyond that DNS servers are not just a "database" of records, they are services that can return different results depending on who queried. And this is quite common with CDNs.

There are many more reasons, but let's talk about what you could do.

You could download a list of all registered domains, and then query all of them for the most common records. It would take hours, not include 99.9 percent all records, and be out of date the second it completes. With this database, you could visit some websites, but many host services on subdomains and you have no way to dynamically get that list when you're populating the database.